Cyril of Alexandria on the Incarnation
Here is another quote by Cyril of Alexandria on the Incarnation, from Faith and Life:
We do not say that the nature of the Word was transmuted and became flesh’, nor that it was converted into an entire man, composed of soul and body; but rather this :—that the Word personally united to Himself flesh animated with a reasonable soul, and became Man, ineffably and inconceivably. Although the natures which were combined into a real unity are diverse, yet from both results one Christ and Son; not as if the difference of the natures had been annulled because of the unione, but rather that Godhead and Manhood, through the ineffable and inexplicable concurrence into unity, constitute for us the one Lord and Son Jesus Christ. Thus it is that although He had His existence before the ages, and was begotten of the Father, He is said to have been born of a woman after the flesh: not that His Divine nature received a beginning of existence in the Holy Virgin, or needed for its own sake a second generation, after that from the Father; but since for us, and for our salvation, He personally united Manhood to Himself, and came forth from a woman, in this sense He is said to have been corporeally born. For it was not that He was first born as a mere man from the Holy Virgin, and then the Word descended upon Him”; but He was from the very womb united to flesh, and so is said to have undergone corporeal birth, in that He claims as His own the birth of His own flesh. In the same sense we say that He suffered and rose again; not that the Word of God in regard to His own proper nature suffered the blows or the piercing of the nails, or the other wounds, —for the Godhead is impassible, because it is incorporeal ; but because that body which had become His very own suffered these things, therefore is He said to have suffered for us. For the Impassible was in the suffering body. In like manner also do we view His death. Thus we confess one Christ and Lord ; nor as worshipping a man together with the Word, but as worshipping one and the self-same, because His body is not alien from the Word, and with His body He sits on the throne with the Father. It is not that two Sons sit on that throne, but One, by virtue of union, with His very own flesh. We must not therefore divide the one Lord Jesus Christ into two Sons. Scripture says not that the Word united to Himself the person of a man, but that He became flesh—which is nothing else than that, just like ourselves, He partook of flesh and blood. He made our body His own, and proceeded, being Man, from a woman, not having cast away His Divine existence and His generation from God the Father; but having continued, while He assumed our flesh, to be what He was. This is what the doctrine of our correct faith every where proclaims.
–St. Cyril of Alexandria, Second Epistle to Nestorius
If I am not mistaken this letter would have been written to Nestorius sometime before the Council of Ephesus in 431.