Christ God and Man by St. Cyril of Alexandria.

” We shall say to them the words of the Saviour; “You err, knowing neither the scriptures nor the power of God” (Matt. 22:29).
You ought to sober up and stop sinning because you have become sick through ignorance of God. We, on the other hand, understand rightly the glory of the union, as it has been handed down, and perceive him to be God eternally and also to have become man in the last times, his divinity protected from change and alteration, and so, we also believe that he was the Savior at the time of Israel’s march out of Egypt. He is eternally the Logos and Light and Brightness of the Father, and he possesses the sovereignty of the God-befitting glory.
Therefore, he also said to blessed Moses, “I am who I am” and “I am the God of Abraham, and the God of Isaac, and the God of Jacob” (Ex. 3:14, 6). He assumed the name of Son, when he became man because of the union and not because he dwelt in a man. Consequently, the divinely inspired Scripture glorifies him by relating the name Jesus Christ both to the past and to the present.”

Cyril of Alexandria,
Against those who are unwilling to confess that the Holy Virgin is Theotokos 6.