The Enchiridion by St. Augustine
Chapter 25.--God's Judgments Upon Fallen Men and Angels. The Death of the Body is Man's Peculiar Punishment.
And yet such a nature, in the midst of all its evils, could not lose the craving after happiness. Now the evils I have mentioned are common to all who for their wickedness have been justly condemned by God, whether they be men or angels. But there is one form of punishment peculiar to man -- the death of the body. God had threatened him with this punishment of death if he should sin, leaving him indeed to the freedom of his own will, but yet commanding his obedience under pain of death; and He placed him amid the happiness of Eden, as it were in a protected nook of life, with the intention that, if he preserved his righteousness, he should thence ascend to a better place.