City of God

It may perhaps be supposed that because God said, “You shall die the death,” and not “deaths,” we should understand only that death which occurs when the soul is deserted by God, who is its life; for it was not deserted by God, and so deserted Him, but deserted Him, and so was deserted by Him. For its own will was the originator of its evil, as God was the originator of its motions towards good, both in making it when it was not, and in remaking it when it had fallen and perished.

But though we suppose that God meant only this death, and that the words, “In the day you eat of it you shall die the death,” should be understood as meaning, “In the day you desert me in disobedience, I will desert you in justice,” yet assuredly in this death the other deaths also were threatened, which were its inevitable consequence. For in the first stirring of the disobedient motion which was felt in the flesh of the disobedient soul, and which caused our first parents to cover their shame, one death indeed is experienced, that, namely, which occurs when God forsakes the soul.

(This was intimated by the words He uttered, when the man, stupefied by fear, had hid himself, “Adam, where are you?” — words which He used not in ignorance of inquiry, but warning him to consider where he was, since God was not with him.) But when the soul itself forsook the body, corrupted and decayed with age, the other death was experienced of which God had spoken in pronouncing man's sentence, “Earth you are, and unto earth shall you return.” And of these two deaths that first death of the whole man is composed.

And this first death is finally followed by the second, unless man be freed by grace. For the body would not return to the earth from which it was made, save only by the death proper to itself, which occurs when it is forsaken of the soul, its life. And therefore it is agreed among all Christians who truthfully hold the Catholic faith, that we are subject to the death of the body, not by the law of nature, by which God ordained no death for man, but by His righteous infliction on account of sin; for God, taking vengeance on sin, said to the man, in whom we all then were, “Dust you are, and unto dust shall you return.”