John 1:14
If they say that being God, He is Omnipotent, so that He could lower Himself to the substance of flesh, we will reply to them, that He is Omnipotent as long as He continues to be God. But if He admit of change, change for the worse, how could He be God? For change is far from that simple Nature. Wherefore the Prophet says, “They all shall wax old as does a garment, and as a vesture shall Thou roll them up, and they shall be changed; but You are the same, and Your years shall not fail.” For that Essence is superior to all change. There is nothing better than He, to which He might advance and reach. Better do I say? No, nor equal to, nor the least approaching Him. It remains, therefore, that if He change, He must admit a change for the worse; and this would not be God. But let the blasphemy return upon the heads of those who utter it. Nay, to show that he uses the expression,'“was made” only that you should not suppose a mere appearance, hear from what follows how he clears the argument, and overthrows that wicked suggestion. For what does he add? “And dwelt among us.” All but saying, “Imagine nothing improper from the word 'was made'; I spoke not of any change of that unchangeable Nature, but of Its dwelling and inhabiting. But that which dwells cannot be the same with that in which it dwells, but different; one thing dwells in a different thing, otherwise it would not be dwelling; for nothing can inhabit itself. I mean, different as to essence; for by an Union and Conjoining God the Word and the Flesh are One, not by any confusion or obliteration of substances, but by a certain union ineffable, and past understanding. Ask not how; for It was made, so as He knows.”
What then was the tabernacle in which He dwelt? Hear the Prophet say; “I will raise up the tabernacle of David that is fallen.” It was fallen indeed, our nature had fallen an incurable fall, and needed only that mighty Hand. There was no possibility of raising it again, had not He who fashioned it at first stretched forth to it His Hand, and stamped it anew with His Image, by the regeneration of water and the Spirit. And observe I pray you, the awful and ineffable nature of the mystery. He inhabits this tabernacle for ever, for He clothed Himself with our flesh, not as again to leave it, but always to have it with Him. Had not this been the case, He would not have deemed it worthy of the royal throne, nor would He while wearing it have been worshipped by all the host of heaven, angels, archangels, thrones, principalities, dominions, powers. What word, what thought can represent such great honor done to our race, so truly marvelous and awful? What angel, what archangel? Not one in any place, whether in heaven, or upon earth. For such are the mighty works of God, so great and marvelous are His benefits, that a right description of them exceeds not only the tongue of men, but even the power of angels.
Wherefore we will for a while close our discourse, and be silent; only delivering to you this charge, that you repay this our so great Benefactor by a return which again shall bring round to us all profit. The return is, that we look with all carefulness to the state of our souls. For this too is the work of His lovingkindness, that He who stands in no need of anything of ours says that He is repaid when we take care of our own souls. It is therefore an act of extremist folly, and one deserving ten thousand chastisements, if we, when such honor has been lavished upon us, will not even contribute what we can, and that too when profit comes round to us again by these means, and ten thousand blessings are laid before us on these conditions. For all these things let us return glory to our merciful God, not by words only, but much more by works that we may obtain the good things hereafter, which may it be that we all attain to, through the grace and lovingkindness of our Lord Jesus Christ, by whom and with whom, to the Father and the Holy Ghost, be glory for ever and ever. Amen.
Source: Homilies on the Gospel of John (New Advent)