Abstract: This book addresses the question of whether the fifth-century pronouncements about Christ's person were reflective of a genuine theological consensus in the early Church, or whether they were merely the result of political pressure or compromise between opposing christological ‘schools.’ The book seeks to use the concept of grace to clarify the question of christology. The study finds that for Theodore of Mopsuestia and Nestorius, grace is God's gift of co-operation to Christians as we seek to advance from the current age to a perfect future age, and Christ is the supreme example of this co-operative grace. In contrast, Cyril of Alexandria views grace primarily as God's gift of himself to Christians by sharing with us the communion he has within himself, between the persons of the Trinity. This view of grace leads Cyril to argue that Christ must be the Son of God by nature in order to give grace to us. Furthermore, this study finds that Cassian holds to a view of grace very similar to that of Cyril. In the light of this connection between grace and christology, the book argues that the central issue of the christological controversy was whether God the Logos was himself personally present on earth through the incarnation. The study concludes by treating several other important writers from the christological controversy, and by suggesting that Cyril's understanding of grace and christology was not merely his own, but was in fact the consensus of the early Church.

Keywords: John Cassian, christology, Cyril of Alexandria, double birth (of the Logos), grace, incarnation, Nestorius, personal subject (of Christ), Presence (of God), Theodore of Mopsuestia