The Only-Begotten became and is called son of man; for this and nought else does St John’s saying that the Word was made Flesh signify.
For it is as though he said more nakedly The Word was made Man.
[…] Man then is a creature rational, but composite: of soul, that is, and of this perishable and earthly flesh.
And when it had been made by God, and was brought into being, not having of its own nature incorruption and imperishableness (for these things appertain essentially to God alone), it was sealed with the spirit of life.
By participation with the Divinity it gained the good that is above nature (for He breathed, it says, into his nostrils the breath of life and man became a living soul).
But when he was being punished for his transgressions, then with justice hearing Dust thou art and unto dust shalt thou return, he was bared of the grace.
The breath of life, that is the Spirit of Him Who says I am the Life, departed from the earthy body and the creature falls into death, through the flesh alone, the soul being kept in immortality, since to the flesh too alone was it said, Dust thou art and unto dust shalt thou return.
It needed therefore that that in us which was specially imperilled, should with the greater zeal be restored, and by intertwining again with Life that is by nature be recalled to immortality.
It needed that at length the sentence Dust thou art and unto dust shalt thou return should be relaxed, the fallen body being united ineffably to the Word that quickens all things. For it needed that becoming His Flesh, it should partake of the immortality that is from Him.
For it were a thing most absurd, that fire should have the power of infusing into wood the perceptible quality of its inherent power and of all but transfashioning into itself the things wherein it is by participation, and that we should not fully hold that the Word of God Which is over all, would energise in the flesh His own Good, that is Life.
For this reason specially I suppose it was that the holy Evangelist, indicating the creature specially from the part affected, says that the Word of God became Flesh —
— that so we might see at once the wound and the medicine, the sick and the Physician, that which had fallen unto death and Him Who raised it unto life,
—that which was overcome of corruption and Him Who chased away the corruption, that which was holden of death and Him Who is superior to death, that which was bereft of life and the Giver of life.
Cyril of Alexandria (c. 376-444): Commentary on John, Book 1, Chapter 9 (on John 1:14) [slightly adapted].