Perhaps, ashamed, they will agree with these things but then say that, if God wished to instruct and save human beings, He should have done so by a mere command, without His Word taking hold of a body, just as He did long ago when He brought them into being out of nothing.
The reasonable reply to their objection is this: in the beginning, when nothing at all existed, a command and the will alone were enough for the creation of the universe. But once humanity existed, and what needed healing was not what did not exist but what had already come into being, it followed that the Physician and Savior should come among things already made, so as to heal what existed. For this reason He became human and used the body as a human instrument.
If this was not the fitting way, how was the Word to come if He intended to use an instrument? And where was He to take that instrument from, except from things already made and in need of His divinity through what was like them? It was not things that did not exist that needed salvation, so that a command alone would suffice; rather, humanity already in existence was being corrupted and destroyed. It was therefore fitting and right for the Word to use a human instrument and extend Himself to all things.
You must also understand that the corruption which had arisen was not outside the body, but had become attached to it. Life therefore had to be joined to the body in place of corruption, so that just as death had come to be in the body, life too might come to be in it.
If death had been outside the body, life too would have had to come to be outside it. But since death had become intertwined with the body and ruled it as though joined to it, life also had to be joined to the body, so that the body, clothed instead with life, might cast off corruption. Even if the Word had been outside the body rather than in it, death would naturally have been defeated by Him, since death has no power against the Life; nevertheless, the corruption that had arisen in the body would still have remained there.
For this reason the Savior rightly put on a body, so that the body, joined closely to the Life, would no longer remain in death as mortal, but, having put on immortality, would rise and remain immortal. For once it had put on corruption, it could not rise unless it also put on Life. And death itself could not appear except in a body. Therefore He put on a body so that, finding death in the body, He might wipe it away. For how could the Lord have been shown to be the Life if He had not given life to what was mortal?
Just as dry stalks are naturally consumed by fire: if someone merely keeps the fire away from them, they are not burned, but they remain what they are—dry stalks—and still fear the threat of fire, since fire naturally consumes them. But if someone clothes the stalks in a thick layer of asbestos, a material said to resist fire, they no longer fear the flames, because the fireproof garment keeps them safe.
The same may be said about the body and death. If death had been kept away from the body by a command alone, the body would still have remained mortal and corruptible according to the nature of bodies. But to prevent this, the body put on the incorporeal Word of God. Thus it no longer fears death or corruption, because it has Life as its garment and corruption disappears within it.