Athanasius would not have used these words in the fourth century, but in this part of his argument (On the Incarnation of the Word, 44:4-8) that the incarnation was essential to our redemption, it seems to me that this is basically what he’s driving at.
4. Secondly, you must know this also, that the corruption which had set in was not external to the body, but had become attached to it; and it was required that, instead of corruption, life should cleave to it; so that, just as death has been engendered in the body, so life may be engendered in it also.
Death and corruption have infected us, and need to be cleaned out by life.
5. Now if death were external to the body, it would be proper for life also to have been engendered externally to it. But if death was wound closely to the body and was ruling over it as though united to it, it was required that life also should be wound closely to the body, that so the body, by putting on life in its stead, should cast off corruption.
Death is woven into our very nature, as if it’s wound around each strand of DNA. In order to be healed of this infection, we need to have life wound around each strand of DNA instead.
Besides, even supposing that the Word had come outside the body, and not in it, death would indeed have been defeated by Him, in perfect accordance with nature, inasmuch as death has no power against the Life; but the corruption attached to the body would have remained in it none the less.
Death is the source of this infection, but we’re already infected with it. Sterilizing the petri dish that contains smallpox doesn’t cure the people who have the disease.
6. For this cause the Savior reasonably put on Him a body, in order that the body, becoming wound closely to the Life, should no longer, as mortal, abide in death, but, as having put on immortality, should thenceforth rise again and remain immortal. For, once it had put on corruption, it could not have risen again unless it had put on life.
So the Savior injected Himself into our bodily condition, thus winding Life as closely through the body as death had previously been wound, and curing us of corruption so that we can rise again to eternal life.
And death likewise could not, from its very nature, appear, save in the body. Therefore He put on a body, that He might find death in the body, and blot it out. For how could the Lord have been proved at all to be the Life, had He not quickened what was mortal?
Death doesn’t manifest except in bodies. So obviously, if He was going to prove that He had overcome death, He had to do it in a body.
7. And just as, whereas stubble is naturally destructible by fire, supposing (firstly) a man keeps fire away from the stubble, though it is not burned, yet the stubble remains, for all that, merely stubble, fearing the threat of the fire — for fire has the natural property of consuming it; while if a man (secondly) encloses it with a quantity of asbestos, the substance said to be an antidote to fire, the stubble no longer dreads the fire, being secured by its enclosure in incombustible matter;
(This is a different analogy, of course, but it is nicely illustrative.)
8. in this very way one may say, with regard to the body and death, that if death had been kept from the body by a mere command on His part, it would none the less have been mortal and corruptible, according to the nature of bodies; but, that this should not be, it put on the incorporeal Word of God, and thus no longer fears either death or corruption, for it has life as a garment, and corruption is done away in it.
If the Lord had simply commanded death to leave us alone, we’d still be susceptible to it. But by means of the Incarnation, the Word was injected into our bodily existence; and so we are rendered immune to corruption. (By means also of the Resurrection, as Athanasius goes into elsewhere in the treatise but I think he’s taking for granted here.) And therefore we can now live as if death were not, as James Alison frequently puts it: we’ve been vaccinated against death, so we can live without worrying about whether we’ll succumb to it.
In the words of the baptismal liturgy,
We have put on Christ,
in Him we have been baptized,