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.]
From his Commentary on Luke:
Our Lord Jesus Christ requires those who love Him to be accurate investigators of whatsoever is written concerning Him: for He has said, "that the kingdom of heaven is like to a treasure hid in a field." For the mystery of Christ is deposited, so to speak, at a great depth, nor is it plain to the many: but he who uncovers it by means of an accurate knowledge, finds the riches which are therein, and resembles that wise woman, even Mary, of whom Christ said, that "she had chosen the good part, that should not be taken away from her." For these earthly and temporal things fade away with the flesh: but those which are divine and intellectual, and that benefit the life of the soul, are firmly established, and their possession cannot be shaken.
From the Second Letter to Nestorius:
For we do not say that the nature of the Word was changed and became flesh, nor that he was turned into a whole man made of body and soul. Rather do we claim that the Word in an unspeakable, inconceivable manner united to himself hypostatically flesh enlivened by a rational soul, and so became man and was called son of man, not by God’s will alone or good pleasure, nor by the assumption of a person alone. Rather did two different natures come together to form a unity, and from both arose one Christ, one Son. It was not as though the distinctness of the natures was destroyed by the union, but divinity and humanity together made perfect for us one Lord and one Christ, together marvellously and mysteriously combining to form a unity. So he who existed and was begotten of the Father before all ages is also said to have been begotten according to the flesh of a woman, without the divine nature either beginning to exist in the holy virgin, or needing of itself a second begetting after that from his Father. (For it is absurd and stupid to speak of the one who existed before every age and is coeternal with the Father, needing a second beginning so as to exist.) The Word is said to have been begotten according to the flesh, because for us and for our salvation he united what was human to himself hypostatically and came forth from a woman. For he was not first begotten of the holy virgin, a man like us, and then the Word descended upon him; but from the very womb of his mother he was so united and then underwent begetting according to the flesh, making his own the begetting of his own flesh.