2.1 The patristic period

In the first centuries of Christianity, the theology of grace was developed as a response to the pastoral and intellectual challenges of the time. It took shape as a ‘developed Christology’ in the context of the deepening of trinitarian and christological doctrine: divine grace is understood as the life of Christ, present in the believer through the action of the Holy Spirit. The Christian writings of the time reflect the awareness that the great ideals of faith, such as martyrdom and virginity, are not realized by human effort alone but primarily by the grace of God, which is identified with Christ (Studer 2007: 2424).

Irenaeus of Lyons, in confronting Gnosticism, stresses the relationship of grace to the incarnation and salvation history. His theology of ‘exchange’ is well-known and is found later in other church fathers: ‘the Son of God became man so that man, united to the Word of God and receiving adoption, might become the son of God’ (Adversus Haereses 3.19.1; Irenaeus of Lyon 2002: 374). Tertullian, following Irenaeus, distinguishes between the ‘image of God’ (the human person created through the Word) and the ‘likeness of God’ (his or her perfection through the Spirit). In this way he enables the distinction between what would later be called ‘nature’ and ‘grace’ as two orders that are related to each other but must not be confused, whose perfection is attained in the incarnate Word (De Baptismo 5.7; Tertullian 2002: 74). Authors such as Tertullian, Clement of Alexandria, Origen of Alexandria, and Cyprian relate grace in a special way to baptism because, through this sacrament, divine life is obtained instantaneously, perfectly, and gratuitously.

Clement of Alexandria, in the second century, was the first to use the term ‘divinization’ to refer to the transformation that takes place in the believer as the fruit of divine action (Protrepticus 11.114.4; Clement of Alexandria 1949: 183). Among the biblical texts on which the fathers usually base the concept of divinization are Ps 82:6: ‘I say, You are gods, children of the Most High, all of you’ and 2 Pet 1:4: ‘you become partakers of the divine nature’ (Mosser 2005). Athanasius, Didymus the Blind, and the Cappadocian Fathers (Gregory of Nazianzus, Gregory of Nyssa, and Basil of Caesarea) use the term when confronting the Arian and Macedonian heresies. They argue that, if the Son and the Holy Spirit were not divine in the full sense, the salvation of the human creature would be impossible, because the one who is not God cannot divinize. Divinization implies liberation from death and corruption, but also adoption as sons and daughters of God. Some scholars affirm that a soteriological motivation can also be found in Arian teachings (Gregg and Groh 1981).

Several early Christian authors, when referring to the action of divine grace, consider its relation to freedom. Gregory of Nyssa deals in a particular way with the cooperation (synergeia) between the divine gift and human effort. Grace is added to human action and not vice versa; it is more powerful than the latter. On the other hand, Ambrose of Milan, following Athanasius, considers that the redemption of Christ is necessary due to the felix culpa, the ‘happy fault’ of humans. Adam, having lost grace, transmits sin to his descendants, and therefore the divine gift is necessary for the first conversion (Apologia David 1.11.56; Ambrose of Milan 1977: 150–152).

Augustine of Hippo is the author who ends up having the greatest influence on the understanding of grace in the West. His doctrine is known mainly from the polemical works he wrote towards the end of his life in a Pelagian context. In them he deals with the relationship between grace and human freedom wounded by sin. However, his contribution cannot be reduced to the healing aspect of grace, because, among other reasons, his doctrine presupposes the development of the preceding fathers, in particular the themes of indwelling, divinization, and communion with Christ. Augustine did not write a systematic treatise on grace, but he referred to grace in the most varied contexts throughout his life, as a consequence of his Christian experience, his speculative reflection, and the pastoral challenges of the time. In his work Ad Simplicianum (c. 397), Augustine affirms that grace is necessary even in the beginning of faith. This intuition would be decisive in his thought because it would lead him to conclude that every salvific act depends on divine grace as an interior light and efficacious force. In the Confessions he expresses this as a prayer addressed to God: ‘grant what you command, and command what you will’ (10.29.40; Augustine of Hippo 1896: 256 [vol. 1]; Drecoll 2010; Harrison 2006).

According to Augustine, divine grace is a reality that believers experience as being loved by God and thus constituted as ‘his lovers’ (De spiritu et littera 32.56; Augustine of Hippo 1913: 214). The Holy Spirit in giving himself produces a real interior effect in humans that brings about the fulfilment of whatever external moral influence there may have been (preaching, good example, etc.). A fundamental text in Augustinian doctrine is Rom 5:5: ‘the love of God has been poured into our hearts through the Holy Spirit who has been given to us’. Augustine comments on it many times (La Bonnardière 1954). He describes the salvific relationship with God not only in individual terms but, in so far as believers are inserted into the ‘whole Christ’, in communion with the head and his members (In Evangelium Ioannis tractatus 28.1; Augustine of Hippo 1954: 277). As the fruit of baptism, the Holy Spirit dwells in the soul of the just and through him, Christ lives, loves, and suffers in those who believe. Consequently, the Father is also present and therefore ‘the entire Trinity lives in us’ (De Trinitate 15.18.32; Augustine of Hippo 1968: 508). Augustine underlines the moral and spiritual aspects of the divine life in the human person. Christians need the repeated promptings of grace to overcome the overwhelming force of sin, yet God not only helps them to act well but also gives the good act itself, in keeping with Paul’s statement: ‘for it is God who works in you to will and to act according to his good pleasure’ (Phil 2:13).

The so-called ‘Pelagians’, on the contrary, emphasize human freedom and a native capacity not to sin. Recent research avoids considering the ideas of Pelagius, Celestius, and Julian of Eclanum under the same title of ‘Pelagians’ and tends to re-evaluate the positions of these authors (Bonner 1999; Löhr 2015). According to Augustine, the ‘Pelagians’ claim that original sin is transmitted by imitation of Adam’s bad example. Augustine considers that this position empties the mystery of redemption and of the solidarity that humankind has with Christ. Grace is necessary to free us from evil and sin, and, by acting in us as charity, it does not violate our freedom (De gratia Christi et de peccato originali 1.13.14; Augustine of Hippo 1902: 136–137). The gentleness of divine love draws our will towards the good not by means of an external constraint but because it arouses an interior decision which is the fruit of the presence of the Holy Spirit in the soul. The works of the just, moved by grace, are free and meritorious, which is why Augustine exclaims: ‘may God conquer you and then you are free’ (In Evangelium Ioannis tractatus 41.10; Augustine of Hippo 1954: 363). The sixteenth Council of Carthage (418) and the second Council of Orange (529) settled these questions in line with Augustine’s thought.

Among the authors of later centuries, Pseudo-Dionysius stands out. He describes the action of grace as a purification, illumination, and union of the believer who ascends to the transcendent God in an experience that dispenses with any sensory or intellectual activity (De Andia 2022). Maximus the Confessor adds the centrality of charity to the negative way of Pseudo-Dionysius, while relating it to the cross of Christ (Garrigues 1976).

2.2 Medieval times

Peter Lombard, interpreting Augustine in the Sentences, states that the virtue of charity may simply be identified with the Holy Spirit at work in those who are in charity. According to him, the Holy Spirit is the love by which we love God and neighbour (I Sententiarum, d. 17, c. 1, aa. 1–2). This understanding of grace and charity is not generally accepted by later medieval theologians, such as Albert the Great, Bonaventure, and Thomas Aquinas, because it would mean that it is not we who love God but the Spirit within us. It does not seem to sufficiently respect the distinction between divine and human action. Thus, the distinction between uncreated grace (God himself given to a creature) and created grace (the effect of this action produced by God’s presence in the soul) begins to be consolidated. Medieval authors began to explain the life of grace and its integration with human nature with the aid of new philosophical categories, especially Aristotelian ones, while still using Platonic categories such as that of participation.

Thomas Aquinas deals with grace at different points in his Summa Theologiae. In the prima pars (first part) he refers to it above all in his treatment of predestination, the missions of the divine persons and trinitarian indwelling. In the prima-secundae (the first part of the second part), at the end of the treatise on fundamental moral theology, he devotes several specific articles to the subject (I-II: 106–114), in the light of the last end of the human person, that is, eternal life. In the tertia pars (third part) he deepens the understanding of grace as the grace of Christ which is received through the sacraments. The biblical commentaries are also important for the understanding of his doctrine (Spezzano 2015; Torrell 2017).

Duns Scotus applies to grace the medieval distinction between potentia Dei absoluta (the unconfined range of possibilities of doing things that God is capable of with no limits of any kind) and potentia Dei ordinate (the divine action that encounters what has already been established at creation). He concludes that, on the basis of the former, God is not obliged to grant grace through the sacraments, even though, by virtue of the latter, he acts in keeping with the commitment made in creation and redemption. Scotus’ position emphasizes the absolute gratuitousness of divine action and the possibility of acting without the need to employ created categories (Reportatio I, q. 1). In the late Middle Ages, William of Ockham’s nominalism was particularly influential (Farthing 1988). According to him, what God does usually falls into the category of potentia Dei absoluta. God gives grace only because he wants to do so, without our being able to understand the meaning or the modality of his action (Quodlibetal questions VI, q. 1, aa. 1–2.4).

Gregory Palamas is the main representative of Byzantine orthodox theology in the fourteenth century. His most important work is Theophanes. In it, one can perceive the attempt to shift the focus from created grace to uncreated grace. Palamas reflects in a particular way on the doctrine of divinization. He affirms that God in his essence (ousia) is completely inaccessible and unknown. What we receive with grace are the ‘divine energies’, uncreated forces distinct from the divine essence. This is not an operative presence of the cause in the effects, but an illuminating reality that arises eternally from the Trinity. The distinction between essence and energies, in his view, avoids compromising divine transcendence when speaking of grace (Theophanes; Gregory Palamas 1865: 929). The Roman Catholic Church has not made any pronouncement on the Palamite doctrine, which is considered authoritative among Christians of the Eastern Orthodox tradition.

2.3 Lutheranism and the Council of Trent

The various doctrines of grace in the late Middle Ages decisively prepared the way for a profound change in the understanding of grace within Western Christianity, which took place on the one hand with Martin Luther and the Reformation and on the other hand through the Council of Trent.

The doctrine of justification by faith is at the heart of the Lutheran confession. Justification is the work of Christ and his grace alone, and is received through a fiducial faith in God that works in us, but without us. The righteousness thus obtained is not susceptible to appropriation by the human creature, because God considers us righteous by virtue of the merits of Christ. However, our sinful condition is not substantially changed by the reception of grace, so that there is no room for any human merit. Nevertheless, divine gracious action in the sinner must manifest itself in abundant good works, Luther teaches, even though the renewal of the human person will only take place in end-time. Ultimately, justification takes place on account of the believer’s confidence in being continually saved by God (Bayer 2007; Mattes 2014; O'Callaghan 2017).

John Calvin takes up the Lutheran doctrine of justification by faith and rejection of merit. He emphasizes the doctrine of predestination, understood as the eternal divine plan of salvation or condemnation. At the same time, Calvin stresses the need for personal and social conversion. Still, the renewal of the Christian takes place through the action of the Holy Spirit and good works are the natural fruit of faith. Salvation by grace denotes the Spirit’s uniting the believer to Christ, and from Christ the believer receives both justification and sanctification. As Calvin says in his Institutes of the Christian Religion, ‘we must understand that as long as Christ remains outside of us, and we are separated from him, all that he has suffered and done for the salvation of the human race remains useless and of no value to us’ (3.1.1; Calvin 1960: 537). Good works enable the growth of the Kingdom of God and are considered a sign of divine favour and predestination. It is perhaps this understanding of predestination that separates Calvinists from the greater part of the Christian tradition (Billings 2007; Gaffin 2016).

The Council of Trent (1545–1563) was convened to overcome the perceived doctrinal errors of the time and to bring about the reform of the church. At the sixth session, a decree on justification was promulgated, which took the Lutheran position very much into account (Folan 2022). Yet it constituted a veritable treatise on grace, an obligatory point of reference for the study of the subject (Denzinger 2012: 1520–1583). The decree recalls that humans, after Adam’s sin, have been separated from God and, although they have not lost their free will, they are completely unable to recover grace on their own strength. Christ was sent for the redemption of all, although his merits are applied only to those who accept him. Whereas Lutherans on the whole took it that justification was external or ‘forensic’, Trent’s decree affirms that ‘justification itself is not a simple remission of sins, but a sanctification and renewal of the inner man by the voluntary reception of grace and gifts’ (Denzinger 2012: 1529).

Although the positions of Lutherans, Reformed, Anglicans, and Catholics on justification have remained in tension for centuries, ecumenical dialogue after the Second Vatican Council has led to a remarkable rapprochement, especially on the basis of a renewed study of the biblical basis of justification. On 31 October 1999 a ‘Joint Declaration of the Catholic Church and the Lutheran World Federation on Justification’ was signed in Augsburg, accompanied by an ‘Official Joint Declaration’ and an ‘Annexe’. This declaration was also signed by the World Methodist Council in 2006, by the Anglican Consultative Council in 2016, and by the World Communion of Reformed Churches in 2017. It is a particularly relevant document because it reaches a ‘notable convergence concerning justification’ (1999: number 13), allowing one to conclude that the mutual condemnations that took place in the sixteenth century have been overcome, even if on some points there is still not complete agreement. In any case, there is agreement on the essentials: ‘Together we confess: By grace alone, in faith in Christ’s saving work and not because of any merit on our part, we are accepted by God and receive the Holy Spirit, who renews our hearts while equipping and calling us to good works’ (1999: number 15).

2.4 Modern and contemporary times

In the period after Trent, reflection focused above all on the relationship between grace and freedom. The so-called controversy De auxiliis, at the end of the sixteenth century, stands out. The Jesuit Luis de Molina uses the concept of scientia media (‘in-between knowledge’) to refer to God’s foreknowledge of our response to any particular grace, on which the sufficient graces we receive depend, while the Dominican Domingo Báñez uses the concept of ‘physical premotion’ to explain how God effectively moves human freedom from inactivity to activity. Pope Paul V allowed both positions to continue to be taught, thus confirming the principle of the freedom of Christians in theological matters on which the Church has not pronounced definitively (Torrijos 2022).

Two authors from the sixteenth and seventeenth centuries, whose interpretation of the Augustinian doctrine is not accepted by the Roman Catholic Church, are also important. According to Michael Baius, grace, charity, and the gifts of original justice are owed to the human persons, so they belong to their created nature. Thus, the gratuity of the divine gift is not clearly understood. According to Baius, after original sin, human nature is corrupted and is incapable of doing any good deed, for its actions are always sinful. Grace now comes as healing and is gratuitous because, as fallen, we are in some way subnatural. Cornelius Jansen takes a similar position, affirming that the human person is currently in a state of decay, but God gives him efficacious grace which it is not possible to resist (Sesboüé 1997: 315–318). As Henri De Lubac reads the history of the issue, an overreaction to Baius led Roman Catholic theologians to distinguish too sharply between nature and grace, and to water down the patristic and medieval teaching that we are capax Dei, that is, that we all have a natural ‘thirst for God’ (De Lubac 1946; 1998).

The post-Tridentine controversies to some extent reflect the absence of a profound biblical and patristic reflection, and the tendency to treat the theme of grace in an objective and individual way, without considering its ecclesial dimension, sacramental and liturgical mediation, or the dynamics of Christian witness. In later centuries a renewal can be observed in authors such as Matthias Joseph Scheeben, who recovers the trinitarian and personalistic dimension of grace, and Henri de Lubac, who opposes the gulf that had opened up in theology between the orders of nature and grace. The liturgical and anthropological reflection of Romano Guardini also contributes to a better understanding of the reality of grace. Significant among the Roman Catholic theologians of the twentieth century, whose impact on the study of the theme of grace has been notable, are Karl Rahner, Hans Urs von Balthasar, and Joseph Ratzinger. Notable among theologians from other confessions who have influenced the Catholic theology of grace are Karl Barth and Wolfhart Pannenberg.

The Second Vatican Council’s Constitution Gaudium et spes takes an important step on the path of renewal in the study of the theme of grace by underlining its profoundly Christological dimension: ‘Christ the new Adam, in the very revelation of the mystery of the Father and of his love, fully reveals man [and woman] to himself and brings to light his most high calling’ (Gaudium 1965: number 22). The doctrine of the universal call to holiness and the sanctification of everyday life promoted by the Council, especially in Lumen gentium, numbers 39–42 (1964), and by the Popes following, deepens the integration of divine grace with the created world. As Pope Francis points out in the Apostolic Exhortation Gaudete et exsultate: ‘We are all called to be holy by living our lives with love and by bearing witness in everything we do, wherever we find ourselves’ (2018: number 14).

3.1 Creation in God’s image and likeness

‘For those whom he foreknew’ evokes the divine work of creation. Creation, as a gift freely willed by God and directed towards Christ as its end and purpose, may be described as ‘grace’ in a broad sense of the term. In that sense, creation is the foundation of God’s plan of grace as applied to the saving work of Christ, made present by the Holy Spirit. The New Testament teaches that God created all things in Christ, through Christ, and for Christ; he is the mediator of salvation because he is the mediator of creation (Col 1:15–20). Creatures depend on Christ as much as they depend on God, therefore grace does not annul what is created but on the contrary brings it to its perfection.

Humans are also created in the ‘image and likeness’ (Gen 1:26) of God and are called to realize their own identity by conforming themselves to Christ, ‘who is the image of God’ (2 Cor 4 :4; Merriell 1990). In the Bible, the terms ‘image’ and ‘filiation’ are closely related. With the word ‘image’ the Old Testament underlines the particular relationship of the human creature to the Creator. This relationship acquires its definitive character in Christ, who perfectly realizes the image as filiation (2 Cor 3:17–18).

Christ brings human nature to fulfilment, considered not only from the point of view of theology but also from the point of view of other sciences. In recent decades, scientific publications that link human psychology with grace have been particularly important. They emphasize the need to consider the human person from an interdisciplinary perspective, distinguishing and integrating what belongs to the field of psychology or psychiatry from what belongs to the field of theology (Emmons et al. 2017; Insa 2023; see Theology and Psychiatry).

3.2 Predestination in Christ

In creating us, says Paul, God ‘predestined us to be conformed to the image of his Son, that he might be the firstborn among many brethren’ (Rom 8:29). Predestination may be described as God’s plan of grace considered from eternity. It has a theological dimension that connotes the absolute priority, freedom, and gratuitousness of the gifts that God offers us. This means that no one can attain grace on his or her own because God’s invitation is always necessary prior to our free response, which it evokes. This is fundamental to the Christian economy.

Predestination also has a Christological dimension, because the first one predestined is Christ; he is ‘predestined already before the creation of the world and manifested at the end of time for your good’ (1 Pet 1:20). Christ is the true predestined one. That is to say, the love of the Father is unerringly directed towards him. In the course of his life, he achieves the end for which the incarnation took place, freely responding to God’s invitation to him. In Christ the destiny of each human person and of all humanity is fulfilled.

Predestination, finally, has an ecclesiological dimension: God predestines Christ, and Christ makes us members of his body, and thus sharers in this predestination. Paul speaks of predestination referring to the church as a whole, as the community of believers. By this he means that Christ infallibly guarantees divine assistance to the church: ‘lo, I am with you always, even to the end of the age’ (Matt 28:20). At the same time, for this assistance to be effective, it must be freely accepted by each individual person. This is why the Catechism of the Catholic Church teaches: ‘For God all the moments of time are present in their actuality. He therefore establishes his eternal design of ‘predestination’ by including in it the free response of each man (and woman) to his grace’ (2003: number 600).

3.3 Vocation, the divine calling

God calls humans, one by one, to participate in his divine life, in his grace. The term vocation refers to the desire for fullness that exists in every single human being from the moment of creation, because ‘from birth man (and woman) is invited to dialogue with God’ (Gaudium 1965: number 12). The divine invitation takes shape according to the concrete circumstances in which each person lives. The Holy Spirit is at work as the one who always calls (klēsis) through the church (ekklēsia) to participate in the life and mission of Christ, and makes the way accessible to him.

3.4 Christian justification

‘And those whom he called, them he also justified’ (Rom 8:30). The divine vocation is realized in the personal history of each person at the moment of passing from the state of sin to the state of grace and adoption, which the New Testament calls ‘justification’. As the Council of Trent points out, justification takes place through faith as one receives baptism or by the desire for it (Denzinger 2012: 1524). Paul affirms that justification takes place by the living faith of Christ and not by works of the law (Rom 3:28; Gal 2:16; 4:6), to underline that it is a completely divine initiative. No human merit can obtain God’s favour independently of grace. The primacy of divine initiative is absolute. At the same time, grace moves humans to free acceptance of and (a kind of) co-operation with the divine action, because justification involves not only the remission of sins but also the sanctification of humans as they are incorporated into Christ through the work of the Holy Spirit.

3.5 Eschatological glorification

‘Those whom he justified he also glorified’ (Rom 8:30), concludes Paul. Heaven is the ultimate horizon which gives meaning to the life of grace that begins with baptism, i.e. to the previous stages of the divine plan, because grace tends towards eschatological fulfilment and is already a beginning of this fulfilment. The resurrection of Christ is at the apex of the new creation or regeneration of creation and is a gift which the Holy Spirit makes present through his action in history, through grace. In the present life, divine grace, although real, remains hidden, but in glory it will be manifested in a clear and luminous way. With grace ‘we walk in faith, not in vision’ (2 Cor 5:7), but, although humans who are still on pilgrimage do not yet ‘see’ God face to face and do not yet have a glorious body like that of the risen Christ, they are already united to him and are transformed inwardly by grace and charity. In that sense there is no substantial difference between the life of grace on earth and the state of eschatological glory. According to Thomas Aquinas, ‘grace is nothing else than a beginning of glory in us’ (Summa Theologiae II-II, q. 24, a. 3, ad. 2; Aquinas 2018).

Understanding grace in the light of its eschatological purpose helps avoid reducing it to a mere ethical aid to overcome sin. Rather it is considered as a reality that already ‘contains’ eternal life in itself by incorporating us into Christ. This ultimate end explains the supernatural character of grace, because attaining eternal life surpasses the natural capacities of any creature. As Augustine points out: ‘the rational creature, angelic spirit or human soul, is made in such a way that it cannot be for itself the good by which it makes itself blessed’ (Epistola 140.23.56; Augustine of Hippo 1904: 202).

4.1 Divine filiation

To understand the doctrine of divine filiation, one must first consider the fatherhood of God. In the ancient Eastern religions among which the people of Israel were established, the term ‘father’ was frequently used to designate certain gods, as was also the case in the classical religions of Greece and Rome. This designation was mainly based on a mythical worldview, according to which human beings were somehow ‘generated’ by the divinity and naturally descended from it. The Old Testament, on the other hand, uses the term ‘father’ frequently, however it applies it almost always to human parents and only rarely to God. The intention is to emphasize the complete divine transcendence of the creator in respect to creation.

While in the Old Testament the term ‘father’ in reference to God is rare, the opposite is true in the New Testament. There, the application of the term to God is noticeably more frequent than the human and profane use of the term. The main reason for the change in the New Testament is not to be sought in a simple reinforcement of the paternal features of divine action, already present in some form in the Old Testament. According to the teachings of Jesus, God behaves as Father because he is, always has been, and always will be Father, because he has a Son consubstantial with himself. The fact that Jesus called God ‘my Father’ is based on a special and unexpected divine revelation of Jesus’ unique filiation (Matt 11:25–27; John 1:18.14).

The divine filiation of Jesus is not merely one more characteristic of his nature; rather it is his deepest identity. He is the eternal Son by nature. The fatherhood of God is expressed at a substantial level in the relationship with his Son. Consequently, any filial relationship to God in the order of creation and in the salvific economy, if verified, cannot but depend on Jesus’ relationship; it necessarily participates in the filiation of the Only-begotten One. Through grace, the Father does not beget other children besides the Son, but by grace he frees us from sin and identifies us with the Son, thus adopting us (Rom 8:23; 9:4; Gal 4:5; Eph 1:5). Christ’s filiation and that of humans are never on the same level, because the Son is that filiation, while humans receive it in time as the fruit of God’s love. They are ‘sons in the Son’ (Mersch 1937: 551).

According to scripture, the interior agent of the Christian’s divine adoption is the Holy Spirit (Rom 8:14–17 and Gal 4:5). The action of the Spirit does not add any thematically-different or new content to the work of Christ. This is how Jesus explains it to the apostles: ‘He will teach you all things and bring to your remembrance all that I have said to you’ (John 14:26; 15:26–27). In the life of the church, the Spirit of the risen Christ carries out what the Son has fulfilled for his disciples on earth, making the eternal love of the Father immediate and tangible (Rom 8:11). Understandably, the work of the Holy Spirit is usually expressed and experienced as something hidden and silent.

Participation in the divine filiation of Christ is the fundamental metaphysical condition of the Christian that gives meaning to every other aspect of the narrative of grace, encompassing it. The virtues and gifts of the Holy Spirit flow from this new condition and are an expression of it. As a result, divine filiation will determine the life of the believer existentially. From it flows the moral and spiritual duty to identify oneself with the life of Christ (Gal 2:20), with his death (Rom 6:8; Col 2:20), and with his resurrection (Col 3:1). The sacraments and Christian prayer intensify divine filiation by allowing believers to participate in the eternal dialogue that takes place within the Trinity. When Christians recite the Lord’s Prayer, they express the awareness of being loved with the same love with which God loves his only Son (1 John 3:1).

The Holy Spirit, by raising us to the condition of children of God in the Son, is the source of a new freedom that gives meaning to mere free will, because the Spirit makes present in believers the ultimate end for which freedom exists – communion with God in eternal life – and makes them capable of directing their lives to him. It gives them the ‘glorious freedom of the children of God’ (Rom 8:21). Divine filiation is also the foundation of a radical equality and fraternity among all human beings, because we all share the same ultimate purpose, regardless of our origin, sex, or profession. Divine adoption ratifies and reinforces love and care for the world we live in. Children of God consider the world created by the paternal hand of God as ‘their own home’. Thus, they live out their ‘secularity’, that is being inserted in the world, with responsibility and filial joy.

Being God’s adopted children implies being ‘co-heirs with Christ’ (Rom 8:17). In other words, divine adoption reaches to eschatological perfection (Rom 8:23–25) which consists in full identification with Christ and the beatific vision: ‘now we are children of God and it has not yet been revealed what we shall be. We know that when he appears, we shall be like him, for we shall see him as he is’ (1 John 3:2).

4.2 Trinitarian indwelling

On the basis of revelation, one can say that God the Father communicates ad intra (in a substantial and necessary way) in the generation of the Son and the breathing forth of the Holy Spirit, whereas he communicates ad extra (in a participatory and gratuitous way) in creation and in the gift of grace or divine adoptive filiation, through the divine ‘missions’. God’s action ad extra refers to the undivided action of the Trinity, even though it is not an undifferentiated principle. In creation, the Trinity puts something other than itself outside of itself, whereas in the giving of grace the believer is elevated and introduced into the inner life of the Trinity. In creation the ‘imprint’ of the creator is perceived, because the human person is the image of the Trinity, whereas with grace this filial image is intensified by divine action.

Sacred scripture refers to a new presence of the Trinity in the soul as the fruit of grace, distinct from that which exists in creation: ‘If anyone loves me, he will keep my word, and my Father will love him, and we will come to him and make our abode in him’ (John 14:23). When God gives himself to the Christian in a new way, his presence brings with it participation in the divine nature (2 Pet 1:3–4). Just as within the Trinity, the Father, in and through the Holy Spirit, communicates his whole nature to the Son; when the Holy Spirit gives himself to us, we receive a participation in the divine paternal-filial relationship. When we speak of participation, we refer to a spiritual reality that is obtained in a partial way, in comparison with God who possesses it in a total way. In other words, God does not communicate his very nature to us, because that only takes place between the divine Persons. God, on the other hand, through the action of the Holy Spirit, brings believers to relate to the Father, in Christ, introducing us into the inner life of the Trinity (John 1:18; 14:3).

Christ is formed in the believer, not as one creature within another but because grace reproduces in us in a participated way the dynamic of knowledge and love proper to the intra-trinitarian life. Grace, through the presence of the Holy Spirit, establishes in believers the same love with which the Son loves the Father. This allows them to enter into a personal relationship with God because he is no longer only the source of grace but also the proper object of a new capacity to know and love, through faith and charity. To understand what it means that the Trinity is the proper object of our knowledge and love, it is useful to turn to Thomas Aquinas’ explanation in the Summa Theologiae. First of all, Aquinas points out that God is present in us ‘as the object known is in the knower, and the beloved in the lover [...]’ (I, q. 43, a. 3, c.; Aquinas 2018). By this he attempts to emphasize that the divine presence in the human soul does not eliminate otherness; believers do not ‘become’ God. Rather, as when we know an object, such as a tree, its interior presence does not transform us into a tree, so there is no ontological mixture between God and the creature raised by grace. Then Aquinas adds:

[...] And since the rational creature by its operation of knowledge and love attains to God Himself (attingit ad ipsum Deum), according to this special mode God is said not only to exist in the rational creature but also to dwell therein as in His own temple. (I, q. 43, a. 3, c.; Aquinas 2018)

In this way Aquinas intends to emphasize that God’s intentional presence in believers does not go far enough. God is not a ‘Platonic love’ for humans, an ideal presence with which we never enter into a real relationship. The gift of the Trinity to the Christian’s soul brings with it a regeneration that allows us to ‘touch’ God in a personal, filial way. That is why, ‘by the gift of sanctifying grace (gratiae gratum facientis) the rational creature is perfected so that it can freely use not only the created gift itself, but enjoy also the divine person Himself’ (I, q. 43, a. 3, ad. 1; Aquinas 2018). In other words, by knowing and loving God we are divinized by Him. Yet God is not ‘enclosed’ in our intellect, which is incapable of comprehending Him, rather it is only with our will that we can love (‘attain’) ‘the whole of God’ and thus establish a friendship with him.

4.3 The metaphysical status of grace

God is love (1 John 4:8) and communicates divine life through the mission of the Holy Spirit (Rom 5:5). Through the action of the Holy Spirit within the believer, grace is received. When God loves humans, he does not love them in the same way as one human person loves another. Our will is moved to love on the basis of an already-existing good in creatures. Human love does not ultimately cause the goodness of the beloved, but presupposes it in the first place. On the other hand, God, in loving a creature, does not find in it a pre-established good in front of which he places himself receptively, but freely gives the good to the creature by creating it and giving it grace. When the Holy Spirit gives his life to the believer, this presence intensifies the natural goodness of the creature to a level that exceeds natural possibilities. Thomas Aquinas in his Commentary on Romans calls this ‘sanctifying grace (gratiam gratum facientem), which is the grace of adoption’ (1, 3, number 46; Aquinas 2020), because the love of the Father poured into us by the Holy Spirit brings about divine adoption, through identification with Christ.

The Holy Spirit enlightens and moves the human heart so that it recognizes its filial condition and gives itself freely, thus corresponding to the love of the Father. When this happens, justification by living faith takes place. In this personal, vital context, God’s grace is perceived as necessary to realize one’s human identity. Through grace, God’s love regenerates the human person from within. Therefore, the result of God’s presence in the Christian is a created reality that embraces the totality of the human being, intensifying its filial condition by acquiring a christological dimension. In this sense, Paul writes that the believer is a ‘new creature’ (Gal 6:15).

Through grace, Christians are divinized without becoming God, for they maintain and increase their ontological autonomy and freedom. The Holy Spirit assimilates them to God by love as soon as they do accept God’s proposal. Because of the ontological difference between creatures and God, the elevation of the human condition is necessary. If, hypothetically speaking, we had a divine nature, it would be natural for us to enter into communion with God. This is not the case, because God transcends every created being, which is why a supernatural gift is needed to regenerate human nature and its faculties. The new state into which the human person is placed by the infusion of grace is on no account an autonomous capacity, for it is constantly dependent on the divine presence in the soul.

Sanctifying grace is an accidental transformation of the person, that is, a qualitative change in who we are, manifested in qualitative changes in what we can do. The use of this Aristotelian term – accident – does not imply that grace is secondary or unimportant; on the contrary, we are aware of the fact that human beings reach their final destination only through divine grace. This concept allows us to avoid the danger of thinking that divinization makes us less human because we are somehow absorbed by divinity. It also enables us to overcome the opposite risk: the possibility of describing the life of grace as something completely external to us. That is, to understand God’s action in us only ‘from the outside’ and grace as an addition that does not really involve us. In this way one would not understand the perfect integration that takes place between the divine and human planes in the person raised up by the divine presence. To speak of grace as an accident or a quality allows us to consider it in the order of efficient causality – God infuses grace – without overlooking formal causality – grace inclines the human person to direct his mind and will towards God – and final causality – God draws the person to himself. In other words, it allows us to emphasize that the human creature is gently and willingly moved by God, in accordance with his nature, to attain the eternal good.

Grace is necessary both to elevate human nature and to heal it. These two effects of grace on the human person are inseparable from one another. On the one hand, those who receive grace are sanctified or divinized by the new condition they are in, that of adoptive divine filiation (the elevating dimension of grace). On the other hand, God’s merciful love frees from sin and progressively heals the wounds caused by the rejection of God (the healing dimension of grace).

4.4 Different kinds of grace

In theology it is not uncommon to speak of different kinds of grace. Grace is one in the sense that the divine action is simple. Thus, from God’s point of view, it makes no sense to make distinctions when referring to grace, because all grace comes from the Father through the Son in the Holy Spirit. However, from the point of view of the one who receives grace, to whom it is not simple, we can and must speak of the different forms that divine gifts take. These correspond, in an approximate way, to the various aspects of the life of the human person itself, elevated by grace. Since grace regenerates the whole human person in its temporal, individual, social, bodily, and spiritual dimensions, to speak of divisions of grace is a simple corollary of the classical adage that grace does not destroy nature but perfects it.

On the basis of the Pauline explanations in 1 Cor 12:7–13:13, Aquinas speaks of ‘sanctifying grace’ (gratia gratum faciens) and ‘gratuitous grace’ (gratia gratis data; Summa Theologiae, I-II, q. 111, a. 1). The former is intended to sanctify the individual directly, while the latter is a divine gift that is received in order to fulfil the mission of the church, i.e. it is a charism given to someone to be used for the common good.

Sanctifying or habitual grace, as described in the Catechism of the Catholic Church, is the ‘permanent disposition to live and work according to the divine vocation’; actual graces, on the other hand, ‘designate divine interventions which are at the origin of conversion or in the course of the work of sanctification’ (Roman Catholic Church 2003: number 2000). Habitual grace is more than mere divine assistance in carrying out a good work, it is that which allows us to enter into the inner life of the Trinity by divine adoption. It may be lost through grave sin but can be recovered through the sinner’s contrition and God’s forgiveness, in virtue of the infinite merits of Christ. In the proper sense of the term, grace is habitual grace, divine life in the believer. Habitual grace encompasses both sanctifying grace (which penetrates the essence of the soul), and the infused theological virtues (faith, hope, charity) and infused moral virtues (prudence, justice, fortitude and temperance) that flow from sanctifying grace, as well as the gifts of the Holy Spirit, the fruits and beatitudes, which penetrate the powers of the soul. Actual grace, on the other hand, is a transitory help that moves believers to perform specific acts. It can intervene before or after justification, however its purpose is not to introduce us into the life of the Trinity but rather to lead us to desire it and to dispose us to it.

The human person, as a social being, can receive from God ‘gratuitous grace’. The term refers to the Gospel text which says: ‘you have received freely, give freely’ (Matt 10:8). This passage from Matthew’s Gospel is at the heart of Jesus’ discourse on the mission of the twelve apostles and speaks of the special gifts given by God to the disciples to facilitate their mission (healing the sick, raising the dead, cleansing lepers, casting out demons, etc.). These are charisms whose specific purpose is to facilitate the mission of the church. These gifts are received for the benefit of others, not for one’s own benefit, and are therefore distinguished from sanctifying grace. The fact of receiving a gift or charism does not automatically make the one who receives it holier than the one who has not received it; rather, it facilitates and obliges to a greater extent the spreading of the gospel. By exercising this duty, it is possible to grow in holiness, but indirectly, so to speak. As Paul points out, we are all called to holiness, but we do not all carry out the same mission in the church as we do not all receive the same charisms. Charisms are effective to the extent that they promote the greatest of God’s gifts, that of charity. Paul insists on the superiority of charity over other special charisms such as speaking in tongues or prophecy (1 Cor 12:31–13:13).

The Christian’s union with Christ cannot be lived out in an individualistic way, because in Christ the whole of humanity is present. As Paul affirms, those who have been renewed by the Holy Spirit feel the need to ‘bear witness to the Gospel of the grace of God’ (Acts 20:24). God gives himself to each believer for his or her own sanctification, but this is destined to be communicated to others. Paul uses the image of the body (1 Cor 12:7–30; Rom 12:3–8; Eph 4:9–13) to express the individual and ecclesial dimensions of grace. The unity of the body in the diversity of functions reflects the fact that each one participates in his or her own way in the church and that the personal response has an impact on the good of all. The ‘communion of saints’ (also understood as a communion of holy goods among the baptized) is a fundamental aspect of the doctrine of grace (Ladaria 2014: 440).

5.1 Freedom and merit

The term ‘merit’, in common parlance, relates to the reward or punishment due for a good or bad deed. At first glance, it seems impossible that humans can ‘deserve’ anything from God, because they have received everything from Him. That is why, strictly speaking, there is no ‘right’ to merit before God. That is to say, we cannot demand ‘payment’ from God for our good deeds. At the same time, this does not mean that He is indifferent to our works and response.

Sacred scripture repeatedly alludes to the reward due to our actions on earth:

And he said to them, ‘Truly, I say to you, there is no one who has left house or parents or brothers or sisters or wife or children for the kingdom of God, who will not receive much more in this time, and in the age to come eternal life’. (Luke 18:29–30; see also Matt 5:11–12; 1 Cor 9:24; Phil 3:14; 2 Tim 4:8)

On the other hand, the Lord, at the conclusion of the parable of the labourers working in the vineyard who receive the same wage for unequal work, expressly asserts: ‘Can I not do with my own what I will, or will you look askance at my being good?’ (Matt 20:1–16).

Some fathers of the church, such as Tertullian, Cyprian, Cyril of Jerusalem, and Augustine, began to speak of ‘merit’ by applying it to the good works of the Christian. Augustine is the one who gives the key to understand how to make a proper use of the term when, referring to God, he affirms: ‘therefore he crowns you because he crowns his own gifts, not your merits’ (Enarrationes in Psalmos 102.7; Augustine of Hippo 1956: 1457). In other words, the essence of ‘merit’ lies in the fact that God associates the human person with the work of his grace. That is why Christian theology has always understood that the only one who has truly merited is Christ. Christians can merit therefore only if they are united to Christ, only if they first of all accept grace. The grace of Christ in us is the ultimate source of merit because it is the only way through which our upright human acts have a supernatural and therefore meritorious character.

Divine free action always precedes and impels human action on a supernatural plane, so that merit is attributed in the first place to divine grace and only in the second place to the human creature. Precisely because merit responds to the free and gratuitous action of God, the first grace that is at the beginning of conversion and justification and final perseverance can never be merited. On the other hand, under the action of the Holy Spirit and charity it is possible to merit all that it is lawful to desire: eternal life, growth in grace and temporal goods, etc., which are obtained according to God’s providence and wisdom.

From the point of view of the human creature, in order to speak of an act being meritorious it is necessary that it is done freely. On the other hand, only those who are on earth can merit. The life of grace may be intensified by the free acceptance of the divine action in us and be translated into abundant good works. At death we will be judged and rewarded according to our works, but both the good we do and the reward we receive will always be a divine gift (Matt 16:27; Rom 2:6; 14:10–12; 1 Cor 3:8). Divine grace and human freedom interact in a mysterious way, interpenetrating and growing together. God’s action in the Christian can never be a source of self-sufficiency or presumption, but rather one of gratitude and humility. Mary is the model of a free and generous response to God’s singular action in her, which is why she is the one who was most meritorious during her life on earth (Hütter 2012: 249–282).

5.2 Experience of grace and created mediations

One might naturally wonder whether it is possible to experience grace or if it is rather a leap into the void. It is clear that an irrational or voluntaristic response to the mystery of God does not respect the dynamics of human freedom. Still, in order to accept grace in a fully human and free way, a response is needed from the human person considered in all its dimensions – intelligence, will, imagination, memory, and affections – not only in some of them, as is the case with rationalism or voluntarism.

Before the Second Vatican Council, probably in response to Lutheran Pietism (which at times tended towards subjectivism) and philosophers like Ludwig Feuerbach (who were suspicious of any kind of religious experience) or Friedrich Schleiermacher (for whom ‘religion’s essence is neither thinking nor acting, but intuition and feeling’; 1996: 22), a more apologetic and rational explanation of faith prevailed in Catholic theology. However, this approach was not sufficient, for, as Hans Urs von Balthasar points out, religious experience ‘is indispensable when faith is understood as the encounter of the whole person with God’ (1982: 219). In other words, God, in order to cherish and energize our freedom, allows us, in a truly human way, to experience a reality that is divine.

Neuroscience enables the study of physical effects that the experience of grace could have on the human person. In recent decades a new and developing discipline called neurotheology has emerged. Andrew Newberg, one of its main representatives, defines it in his book Principles of Neurotheology as the ‘field of study linking the neurosciences with religion and theology’ (2010: 45; see Theology and Neuroscience). It is possible to distinguish at least three different approaches to neurotheology. First, there are the physicalists, who consider that only material physical realities exist (Michael Persinger and Kevin Nelson). Second, there are those who emphasize that spiritual experiences cannot be sufficiently explained without some kind of metaphysics or theology (B. Alan Wallace, Eben Alexander, and Mario Beauregard). Finally, some authors present a neutral perspective (Eugene d’Aquili and Andrew Newberg). Neurotheology is a novel and complex discipline which requires a holistic approach that considers the specific field of study that corresponds to the sciences, philosophy, and theology (Cardone 2021).

From a theological perspective, speech about human experience of divine action is justified by the fact that God became incarnate in Jesus Christ. The apostles touched the Word made flesh and this real personal experience has been handed down through the centuries in the church. As the New Testament points out,

what was from the beginning, what we have heard, what we have seen with our eyes, what we have looked upon and touched with our hands concerning the Word of life [...] what we have seen and heard, we declare to you so that you also may be in communion with us. And our fellowship is with the Father and with his Son Jesus Christ. (1 John 1:1–3)

The Holy Spirit at work within believers enables them to have a real personal experience of God’s love (Rom 5:5), similar to that which the apostles had in their personal relationship with the Lord. The church is the vital context in which believers have this experience of Christ. This does not lead Christians to conclude with subjective certainty that they are in the state of grace. Through faith beliers have objective certainty of the salvation which Christ has obtained for them and of the created mediations through which grace is made present in their lives, first and foremost the humanity of Christ. At the same time, the believer trusts that the Holy Spirit dwells in their soul in grace by various signs or effects that could manifest his presence, such as attraction to spiritual things, awareness of not having committed grave sin, the presence in one’s life of works of charity, boldness, and inner peace, identification with Christ on the cross, or active membership in an ecclesial community, to name but a few. When some of these signs are present, it is possible to assume trinitarian indwelling in the soul, without having full certainty of this being the case.

This leads to the question of why God would allow humans to experience uncertainty in respect of something that is of so much weight in our lives, that is his living presence in our soul. It is possible that the uncertainty gives space for our freedom to grow and for our generosity to find expression. If the reception of grace were self-evident, there would be less room for a creative and generous human response. At the same time, the human experience of divine action is not an end in itself. Authentic religious experience is relativized in the face of its end, which is union with God. There is always the danger of idolizing religious experience as a substitute for God, which is why the absence of a sensitive experience of God’s presence in the soul can be a path of inner purification in which hope prevails with its peculiar kind of ‘certainty’, which is confidence.

Ultimately, it is God who saves and gives grace. He has no need of human mediations to communicate his gifts, for he can open his inner life to whomever he wants, when and how he wants, in ways we do not know; however, the tangible mediations of grace find meaning in the only mediator, Christ (1 Tim 2:5), and they correspond perfectly to our nature that is typically tied in with the senses. They corroborate the fact that God not only acts within human interiority but also addresses the whole person, in its spiritual, corporeal, and social being. Such mediations make us aware of our radical otherness and distinction in relation to the creator and of our inability to enter into communion with God by human forces alone. The sacraments are principal mediations of grace which express and realise the configuration to Christ by the action of the Holy Spirit. Chief among them is the eucharist, ‘the source and summit of the whole Christian life’ (Vatican Council II Lumen Gentium 1964: number 11), by which we are incorporated into Christ himself, the author and content of divine grace, through the gift of the Holy Spirit.