1. We have confessed one substance of the Father, of the Son, and of the Holy Ghost, and have agreed that it is immutable. If then there is one substance of the Trinity, and it is immutable, then the only begotten Son, who is one person of the Trinity, is immutable. And, if He is immutable, He was not made flesh by mutation, but is said to have been made flesh after taking flesh.
2. If God the Word was made flesh by undergoing mutation into flesh, then He is not immutable. For no one in his senses would call that which undergoes alteration immutable. And if He is mutable He is not of one substance with Him that begat Him. How indeed is it possible for one part of an uncompounded substance to be mutable and the other immutable? If we grant this we shall fall headlong into the blasphemy of Arius and Eunomius, who assert that the Son is of another substance.
3. If the Lord is consubstantial with the Father, and the Son was made flesh by undergoing change into flesh, then the substance is at once mutable and immutable, which blasphemy if any one has the hardihood to maintain, he will no doubt make it worse by his blasphemy against the Father, for inasmuch as the Father shares the same substance, he will assuredly call Him mutable.
4. It is written in the divine Scriptures that God the Word took flesh, and also a soul. And the most divine Evangelist says the Word was made flesh. We must therefore perforce do one of two things: either we must admit the mutation of the Word into flesh, and reject all divine Scripture, both Old and New, as teaching lies, or in obedience to the divine Scripture, we must confess the assumption of the flesh, banishing mutation from our thoughts, and piously regarding the word of the Evangelist. This latter we must do inasmuch as we confess the nature of God the Word to be immutable, and have countless testimonies to the assumption of the flesh.
5. That which inhabits a tabernacle is distinct from the tabernacle which is inhabited. The Evangelist calls the flesh a tabernacle, and says that God the Word tabernacled therein. |The Word,| he says, |was made flesh and dwelt among us.| Now if He was made flesh by mutation, He did not dwell in flesh. But we have been taught that He dwelt in flesh; for the same Evangelist in another place calls His body a temple. We must therefore believe the Evangelist's explanation and interpretation of what to some seemed ambiguous.
6. If when the Evangelist wrote |the Word was made flesh| he had added nothing which could remove the ambiguity, perhaps the controversy about the passage might have had some reasonable excuse, from the obscurity of the terms used. But since he immediately went on to say |and dwelt in us,| the combatants contend to no purpose. The former clause is explained by the latter.
7. The immutability of God the Word is plainly proclaimed by the most wise Evangelist, for after saying |the Word was made flesh and dwelt among us,| he immediately adds, |And we beheld His glory, the glory as of the only-begotten of the Father, full of grace and truth.| But if, according to the foolish, He had undergone mutation into flesh, He would not have remained what He was, but if even when enveloped in the flesh He emitted the rays of His Father's nobility, it follows that the nature which He has is immutable, and it shines even in the body and sends abroad the brightness of the nature which is unseen. For that light nothing can dim. |For the light shineth in the darkness, and the darkness comprehendeth it not,| as saith the very divine John.
8. The illustrious Evangelist was desirous of explaining the glory of the only-begotten, but was unable to carry out his purpose. He therefore shews it by His fellowship with the Father. For he says He is of that nature; just as though any one to persons beholding Joseph sunk in a slavery inconsistent with his rank, and unaware of the splendour of his descent, were to point out that Jacob was his father, and his forefather Abraham. So in this sense the Evangelist said that when He dwelt among us He did not dim the glory of His nature, |For we beheld His glory, the glory as of the only-begotten of the Father.| So if even when He was made flesh it was plain who He was, then He remained who he was, and did not undergo the mutation into flesh.
9. We have confessed that God the Word took not a body only but also a soul. Why then did the divine Evangelist omit in this place mention of the soul and mention the flesh alone? Is it not plain that he exhibited the visible nature and by its means signified the nature united to it? For the mention of the soul is understood of course in that of the flesh. For when we hear the prophet saying |Let all flesh bless His holy name,| we do not understand the prophet to be exhorting bodies of flesh without souls, but believe the whole to be summoned to give praise in the summoning of a part.
10. The words |the Word was made flesh| are plainly indicative not of mutation, but of His unspeakable loving-kindness. For after the illustrious Evangelist had said |in the beginning was the Word, and the Word was with God and the Word was God,| and had declared Him to be Creator of the visible and invisible, and had called Him life and true light, adding other similar expressions, and had spoken concerning the Godhead in such terms as human reason can take in and the language at its command can express, he went on |And the Word was made flesh,| as though smitten with amazement and astounded at the boundless loving-kindness. His existence is eternal; He is God; He made all things; He is source of eternal life and of true light; and on account of the salvation of men He put about Him the tabernacle of flesh. And He was supposed to be only that which He appeared. So for this reason he did not even mention a soul but only the perishable and mortal flesh. Of the soul as being immortal he said nothing in order to exhibit the boundlessness of the kindness.
11. The divine Apostle calls the Lord Christ seed of Abraham. But if this is true, as true it is, then God the Word was not changed into flesh, but took on Him the seed of Abraham, according to the teaching of the Apostle himself.
12. God swore to David that of the fruit of his loins, according to the flesh, He would raise up the Christ, as the prophet said and as the great Peter interpreted. But if God the Word was called Christ after mutation into flesh, we shall nowhere find the truth in the oaths. Yet we have been taught that God cannot lie; nay rather is Himself the truth. Therefore God the Word did not undergo change into flesh, but in accordance with the promise, took firstfruits of David's seed.