Irenaeus and the Wonderful Exchange

I was looking for a good advent quote to put up on my blog but couldn't find anything that seemed very fitting. As I was flipping through some stuff on my bookshelf I came across a collection of writings by the 2nd Century Christian St. Irenaeus. Irenaeus had been a student of the martyr Polycarp who, in turn, had known the Apostle John. One theme in theology I've become interested in is the idea of a "Wonderful Exchange" which took place between God and man in the life, death and resurrection of Jesus Christ. Luther and Calvin both write on this theme, along with Patristic writers. Irenaeus touches on this theme, perhaps a bit more obliquely than those mentioned, in his most famous work, Against Heresies. Here are a few short quotes which I found interesting:

The Son of God became the Son of Man, so that through Him we might receive adoption. This takes place when man receives and bears and embraces the Son of God.

Spiritual though it was (Rom. 7:14), the law only manifested sin; it did not suppress it, for sin did not hold sway just over the spirit, but over the [whole] man. It was necessary, therefore, that the One who came to slay sin, and to redeem man deserving of death, should become precisely what man is, namely man. It was man who was dragged by sin into slavery and held fast by death, and so it had to be a man by whom sin was slain, a man who went forth from death.

There was no other way for us to receive incorruptibility and immortality than to be united to incorruptibility and immortality. But how could we be united to incorruptibility and immortality without incorruptibility and immortality first becoming what we are, the perishable putting on imperishability, the mortal putting on immortality (cf 1 Cor. 15:54), 'so that we might receive adoption as sons' (Gal. 4:5)?