The Word of God the Father, after all, did not come down into a man as the grace of the Spirit comes down on one of the holy prophets, but he himself truly became flesh, as it is written, that is, he became man. He is indivisible, then, after the union, and he is not divided into two persons, even though we recognize that the Word of God is one thing and the flesh in which he has come to dwell is another. Since the whole chorus of holy apostles confirms for us the faith concerning these matters, in that they say that they have "come to know" that he is "the Christ, the Son of God" in the singular, we will not accept, if we think rightly, those who ignorantly dare to institute something new beyond this.
[Cyril of Alexandria, Commentary on John, Volume I, Maxwell, tr., Elowsky, ed., IVP Academic (Downers Grove, IL: 2013) p. 258.]