Translated by P. E. Pusey
But haply they will say in their folly that the Word being God changed into flesh yet not the whole nor altogether: albeit how is it not an evident proof of utter madness, to think and say that these things are so? for first of all to say that not wholly nor yet altogether did He change or undergo turning pertains to those who mete Him and represent Him as quantitied and no longer incorporeal, yea and capable of being conceived of as in space and as become circumscribed. Next how must not the opponents consider this too, that whatever a part of a body subject to the Word suffer, this full surely the whole too will in possibility suffer? (for suffering would not befall one of the parts, unless the nature of the whole body were susceptible of suffering). Hence seeing that the test of their ideas compels us even against our wills to advance to words we would not, beseeching the Word of God to pardon us we say this: that if it is true that He possesseth not the being beyond turning neither is the suffering it impossible to Him, the force of the blasphemy will full surely reach both to the Father Himself and to the Holy Ghost, for Consubstantial is the Holy and untaint Trinity. And then what stability look we for in God as to our own case if He too is weak as we and undergoes commotion unto what is not lawful to say, albeit we heard Him say in plain terms, Behold I am and have not been changed, the Divinely-uttering Psalmist too says that the Heavens are the works of Thy Hands: they shall perish but Thou abidest and all of them shall wax old as a garment and as a covering shalt Thou fold them and they shall be changed, but Thou art the Same and Thy years shall not fail? Consider therefore that he who in spirit speaketh mysteries and is God-taught flings turning to the nature of things generate, saying by way of illustration or demonstration that the heavens shall wax old, and hath reserved Immutability to the God Who is over all, for he hath testified to Him Ever-being and unchangeableness.
And as it has been believed to be impossible that the Nature of the Word should change into what it was not, so can it not be that the generate pass into the nature of Godhead, lest many of Its attributes be seen to be accidents, which if it advanced so far as idea alone would have the charge of blasphemy indelible. For if ought of things generate at all change into the Godhead by Nature, one would not miss of right reasoning if one should chuse to say that It out of things that are not comes into existence and obtains that which is not its, as a sort of material of Its being, and that the body became the substance of incorporeal Essence, tangible and visible of the Invisible and Untangible. And if the Father's Only-Begotten Word is by Nature Life as being of the Father Who is Life, and by change hath admitted unto consubstantiality (as they say) that which, is of the human lump, there is great fear lest we say that He is not unmixed life, for He is not unmingled with what is apt to decay.
In another way too does the opinion of the deceived ones battle with the Economy with flesh: how, we will say. The Lord being God appeared to us that He might destroy the decay which lorded it over us, not that Himself might exhibit His own Nature partaker with decay by immingling with Himself flesh subject to death.
The charge therefore is of equal force, whether one say that the Word of God have been turned into the nature of body or whether that the flesh again is transformed into consubstantiality with God. It is fit therefore that we keep away from both one and other, seeing that it is not without peril to chuse to think beside what one ought to think.
Reference address : https://www.elpenor.org/cyril-alexandria/against-synousiasts.asp?pg=2