Tertullian

“ Now, if He admits not of being transfigured, it must follow that He be understood in this sense to have become flesh, when He comes to be in the flesh, and is manifested, and is seen, and is handled by means of the flesh; since all the other points likewise require to be thus understood. For if the Word became flesh by a transfiguration and change of substance, it follows at once that Jesus must be a substance compounded of [5] two substances—of flesh and spirit,—a kind of mixture, like electrum, composed of gold and silver ”

“ Jesus, therefore, cannot at this rate be God for He has ceased to be the Word, which was made flesh; nor can He be Man incarnate for He is not properly flesh, and it was flesh which the Word became. Being compounded, therefore, of both, He actually is neither; He is rather some third substance, very different from either. But the truth is, we find that He is expressly set forth as both God and Man ”

“ For whatsoever is transfigured into some other thing ceases to be that which it had been, and begins to be that which it previously was not. God, however, neither ceases to be what He was, nor can He be any other thing than what He is. The Word is God, and “the Word of the Lord remaineth for ever,”—even by holding on unchangeably in His own proper form. ”