Like most of the early Fathers, Cyril made no claims to originality, indeed it was of the essence of his method and belief that he brought nothing new to theology. As he pointed out in a letter to Acacius of Beroea: ‘I have been nurtured at the hands of holy and orthodox fathers;’  and we see, in his use of Origen, St. Athanasius, St. Basil and St. Gregory Nazianzus, that far from possessing the arrogance attributed to him by his detractors, St. Cyril lies firmly in the best patristic tradition of adapting the insights of the past and adding, where appropriate, glosses of his own It was this enormous knowledge of Scripture, and of the exegetical tradition of the Church, which would make him such a formidable defender of orthodoxy in the controversy with Nestorius. So where does Cyril’s importance lie? If he simply wrote long allegorical commentaries of a sort which were once fashionable, but no longer serve any useful purpose, was Gibbon not right about him?
Orthodoxy proceeds by a process which might be described as dialectical in so far as a basic position which has been assumed to be so is challenged, and a debate follows. Yes, the ‘faith’ was ‘once delivered’, but despite the assumptions of some, aspects of doctrine turned out not to be clear. As early as the writing of St John’s Epistle, converts were arguing about whether Jesus was God, and if so, what that meant for the idea of monotheism; how could Jesus be God and God be one? If Jesus was God, was his mother then the mother of God? What did that mean? But what did it mean is Mary was not in some sense the Mother of God. This is where St Cyril made an enormous contribution to our understanding. Instead of simply saying that Jesus was God, but it was all a mystery, and Mary might or might not have been the Mother of God in some sense, Cyril; brought his huge learning and Scriptural knowledge to his job as a Pastor of Souls. His theological writing was designed with one purpose in mind – the salvation of souls. How was man saved? He is saved, Cyril argued, by Christ becoming man. But if He had just become a man, then how would that save us? He must also have been God? But what did that mean? The Incarnation is at the heart of his doctrine of salvation, and for him, any message that detracted from the full humanity and full divinity of the Incarnate Word threatened the salvation of his flock.
An examination of St. Cyril’s comments on St. John’s Gospel give us an insight into the formation of his thought on this important issue.
To our way of thinking, St. Cyril’s Commentary on the Gospel of St. John is an odd one. We are used to commentaries which deal equally with all verses, but this is not the Patristic model. The first book, which when printed covers 168 pages, deals only with St. John 1:1:1-28; the second, which covers 293 printed pages, deals with St. John 1:29-5:34; John 5:35-6:37 are covered in the 116 pages of book 3, whilst book 4 takes 159 pages to comment on John 6:38-7:24; book 5 requires 171 pages to deal with John 7:25-8.43, and it takes him 12 books in all to cover the whole Gospel. So it can be seen that like many of the early exegetes, it is the earlier part of the Gospel which commands most of his attention; he takes three chapters to examine John 1:1 alone, and then another hundred pages to get to verse 28. The Incarnation as described by St. John is at the centre of his thought. Although the modern Western practice is to separate Christology from Soteriology, such a distinction was not only unknown to St. Cyril, it would have run counter to his mode of thinking. The Holy Trinity is at the heart of our salvation, as it is of St. Cyril’s theology.
A key Cyrilline text is St. John 16:15: ‘All that the Father has is mine, therefore I said that He will take what is mine and share it with you.’ In his writings on the Trinity, St. Gregory Nazianzus had used this verse to emphasise that there was nothing which was ‘peculiar’ to any one of the Persons of the Trinity: ‘For their being itself is common and equal, even though the Son receives it from the Father.’  This anti-Sebellian line is also emphasised by St. Cyril using the same verse, when he argues that it shows that the Spirit does not possess His wisdom by participation in the Son. If ‘He will take what is mine’, St. Cyril writes, it is because the Spirit ‘is consubstantial with the Son and proceeds through Him as befits God, who possesses in its perfection all the virtue and all the power of the Son.’ The Holy Spirit is like ‘a living and active fragrance from the substance of God, a fragrance which transmits to the creature that which comes from God and ensures participation in the substance which is above all substances.’ It is interesting that St. Cyril, as so often, uses an analogy which is not connected with the thought processes; by such means he emphasises that through the Spirit we not only receive knowledge of the divine nature, we actually participate in it:
If in effect the fragrance of aromatic plants impregnates clothing with its own virtue and in some way transforms into itself that in which it finds itself, how does the Spirit not have the power, since it issues from God by nature, to give, by itself to those in which it finds itself the communication of the divine nature? [In Jo 11:1-2, dealing with St. John 16:14-16.]
St Cyril eschews mechanistic analogies, and even though he cannot, at times, avoid philosophical and technical terms, he always tries to write about the Trinity in terms which appeal to the empathy of his readers.
 Russell, St Cyril p. 4, note 18, which I have preferred to Fr. McGuckin’s version at p. 339 of his book.
 P. Schaff and H. Wace, A Select Library of Nicene and Post-Nicene Fathers: Series 2, volume VII (Grand Rapids, 1996 edn.), St. Gregory Nazianzen, ‘The Fourth Theological Oration, XI, p. 313.