Cyril's ecclesiastical policies and methods are much debated, but his contribution to Christology is indisputable. The ecumenical councils of Ephesus and Chalcedon are not fully appreciated without understanding Cyril's theology and role in the conciliar proceedings and the later Monophysite defection.
Norman Russell provides a scholarly introduction to Cyril's life and then provides you with snippets of Cyril's Commentary on Isaiah and portions of his Commentary on John. Cyril's actual commentary on John is quite vast, but the selections presented here give you a clear picture of his understanding of the incarnation, the efficacy of the eucharist, the divine and human wills of Christ, the humanity of Christ, the mission of the Spirit and the Unity of Christians. Russell then provides translations of a small, but significant segment of Cyril's Five Tomes Against Nestorius. An Explanation of the Twelve Chapters is complete and received authoritative status at the fifth ecumenical council. Against Julian (the apostate emperor) also gives the reader glances of representative sections. Overall a very fine introduction to Cyril's thought.