Cyril of Alexandria (c. 376 – 444) is arguably one of the most important theologians on the development and clarification on Christology in the Church Tradition. Following on the heels of Athanasius and the Cappadocian Fathers, Cyril was the integral figure in hammering out the heresy of Nestorianism (a rough outline of Nestorianism: the belief that Jesus Christ is composed of two persons or, using Nestorians’ terminology, ‘two sons’–one divine and the other human. This strong dichotomy jeopardizes core tenants of Christianity: the uniqueness of Jesus, salvation brought up by God, the role of the Spirit in believers, etc).
On the Unity of Christ is penned by the mature Cyril amassing and curtly arranging his thoughts in dialectical conversation. Here, Cyril is battling all kinds of heresies: Nestorianism, Arianism, adoptionism, Apollinarianism, and Eutychianism. It is a testament of his superior rhetoric to say so much against so many with such few words. This work, therefore, is an absolute essential reading for Christology.