The argument of this chapter is that the instrument doctrine, if held, sharpens our understanding of other mysteries of the Christian faith, including the hypostatic union, the Church, and the sacrament of the Eucharist. One reason that Aquinas held to the doctrine was the clarity it brought to these other mysteries. With Christology, the benefits are grammatical and speculative. Calling Christ’s humanity an instrument leads us to think of the one who possesses it, namely, the Logos, and so it can render single-subject Christology clearer to the intellect. If Christ’s humanity is held to be an instrument, it also implicates in our understanding the divine power through which the Logos works. With the theology of the Church, the instrument doctrine supports the biblical idea that Christ sends the Holy Spirit on the Church as a human being, and not only as God. And with the theology of the Eucharist, the instrument doctrine assists Catholic faith in perceiving how Jesus gives us a share of the divine life through sacramental communion.

The introduction states the biblical premise of the book’s argument. In Scripture, God saves human beings through the actions and sufferings of Christ in the flesh. St. Thomas Aquinas developed a theological account of the Incarnation that attempts to account for the way Scripture speaks, namely, that Christ’s humanity is the instrumental cause of salvation, or as the book calls it, "the instrument doctrine." The introduction then gives an overview of the book’s argument: this doctrine best accounts for how Jesus Christ saves Christians in virtue of his humanity. It outlines the argument of the seven following chapters.

The chronography of Annianus, composed in 412, stands out by closely mapping the chronology of the world onto the Alexandrian 532-year Easter cycle, of which he may be the originator. He also defended that Christ was born in AM 5500, which had its roots in Christian exegesis. This generated a set of chronological anomalies, especially the fact that he situated birth and death of Christ about 10 years later than usual in Christian chronography. As a consequence, there is hardly any trace of Annianus before the second half of the sixth century, when Justinian’s attempt to impose the Christmas date of 25 December on the church of Jerusalem sparked a controversy. Annianus’ chronology, which supported the date of 25 December, was put forward by the defenders of that date (especially Heron), whilst those defending 6 January drew on Andreas. Due to this controversy, Annianus’ chronography travelled from Alexandria to Constantinople and was transmitted to Syriac and hence into Arabic.

Augustine’s doctrine of the totus Christus, the whole Christ with Christ as Head and the Church as Body, developed within his preaching ministry. The doctrine emerges from Augustine’s prosopological exegesis of the Psalms and grows into a theological reflection on the enduring union of Christ and the Church that leads Augustine to say that Christ and the Church share a voice, an identity, and a life. This transforming union gives Christians a new identity as members of the Body of Christ through the sacraments of baptism and the Eucharist. The life of the Church reflects the love and unity of Christ in its life and action in the world. Because of its deep roots in his preaching, Augustine’s doctrine of the totus Christus can be called a preached theology. That is, it is a theology developed within the context of preaching, both in the preparation for preaching and in the preaching itself.

I address three questions. First, how do Eastern theologians configure the way the incarnation is rendered as God’s original intention, and how significant is that insight? The answer is that this is central to their portrayal of God’s purpose. Second, what precisely is God’s purpose in the incarnation? The answer lies in the notion of deification, our being made divine, a concept pivotal to Eastern theology – and yet one that seems in significant respects problematic. Third, are there ways in which Eastern theologians portray God’s purpose that are less problematic, yet equally integral to their notion of God’s original and constant purpose? The answer is, yes there are. I conclude with three key motifs that I find more transferable yet nonetheless wholly authentic to the Orthodox theological imagination: communion, participation and transfiguration.

The book comes in three parts. In Part I I set out the full extent of incarnational theology, in terms of abundance, relationship, transfiguration and blessing. I explain seven ways in which my account seeks to correct the ways conventional theology departs from a truly theocentric approach. This is a story about God (rather than us). It is a story about Jesus (rather than overcoming sin and death). It is a story of abundance (not deficit). It is a story of God’s sovereignty (not rules God must obey). It is a story about Jesus from the beginning (not just from the annunciation). It is a story of flourishing (not inhibition). It is a story in which God’s means and ends are identical.

This chapter articulates God’s purpose, which could be identified with the term ‘election’, but which here I break down into three themes – incarnation, creation and eschatology. If God’s character is not to change, God’s way of bringing about that purpose must be entirely consistent with the nature of that purpose. Thus the incarnation is both the means and the end of God’s purpose. God’s ultimate purpose is for us to be with God: God achieves that purpose by being with us. The incarnation is God being with us: the eschaton is us being with God. Creation is incarnational, because the purpose of creation is to be the theatre of God’s relationship with humankind, and because Jesus demonstrates what creation is and where it belongs in the story of God. The gospels portray the incarnate Jesus as the one through whom creation turns into heaven, and the flaws in existence are overwhelmed by the foretaste of essence.

Physicalism was a logical development of fourth-century theology, but the fifth-century triumph of the creationist ensoulment model had the effect of making physicalist soteriology a much less useful theological tool by narrowing the possible physicalist effects of the incarnation to the body only (and not the soul). The disappearance of physicalism is one manifestation of the detrimental effect the creationist ensoulment model had on theological conceptions of human solidarity through its sharp division between body and soul that rendered “human nature” a category that no longer had logical relevance as regards articulations of fall or redemption. The renewed interest in both human solidarity and “human nature” as a meaningful soteriological category – manifest most clearly in the current explosion of interest in deification studies – emphasizes the need for a new curation of the Christian tradition that would both restore the category of human nature to soteriological usefulness and would recognize physicalist soteriology as a historical reality that should be evaluated for its possible utility to contemporary needs.

Jesus of Nazareth’s future engages Christian hope and the fulfillment of creation’s purpose. Jesus’s earthly life and divine identity are inseparable. This union both constitutes and challenges perceptions of linear time and functions creatively to intertwine past, present, and future. Jesus’s transformative impact on humanity and history signifies the final reconciliation and realization of God’s kingdom, which is manifest both in his historical presence and in his eternal nature.

St. Paul speaks about the church as the body of Christ, and he also speaks about the Eucharist as the body of Christ. How are these two affirmations related? Christian medieval authors gave consideration to the notion of the church as the “mystical body” of Christ and understood the church as the fruit or result of eucharistic communion in the “true body” of Christ. This chapter examines the thought of Thomas Aquinas on the church and its relation to the sacraments. It also shows how this conception has deeply informed the modern idea of the church as a sign and instrument of grace for all human beings, called to communion in the one Christ.

This chapter considers the ways in which the classical credal and conciliar formulae provide a framework for understanding who Jesus Christ is and how God saves through the Incarnate Word. These credal and conciliar formulae provide the foundation for theologies across the spectrum of Christian traditions. The chapter is broadly divided into two sections, one focusing on the fourth century Trinitarian controversies, the second focusing on the christological controversies of the fifth to the seventh centuries. For classical Christian theology, only when Jesus is known as the Word made flesh, and as one coequal to Father and Spirit in the divine life, can the work of redemption be understood.

If any book could be said to condemn the whole idea of human beings attempting to become like God, then surely it is the Bible. At the very beginning of Genesis, a serpent (later identified as Satan) tempts Eve with the promise that, if she disobeys God by eating of the tree of the knowledge of good and evil, then she will be “as a god.” According to the Bible, the root of all evil is pride; and pride means precisely thinking that we could become divine. Jesus himself is condemned by the Jewish priests for the blasphemous arrogance of claiming to be divine. And yet, the Bible also promises the faithful that they can become “partakers of the divine nature.” What the Bible condemns, of course, is self-deification. If we surrender to God’s love and seek intimate relation to him, God promises to transform us into creatures who possess divine sanctity and everlasting life. The biblical God is less a paradigm of perfection that we might imitate and more a divine person with whom we might have a loving relationship. According to the Bible, we are divinized not by merely imitating God but by loving and being loved by him.

This introduction situates the book within the landscape of contemporary christology, arguing that a non-competitive christology or a “Chalcedonianism without reserve” best accounts for Christ’s human receptivity to the world. This book will develop such an account through the resources offered by Augustine of Hippo’s christology.

This chapter examines Augustine’s account of the eternal God’s creation of, ordering of, and presence within creaturely temporality, a presence perfected in the Incarnation.