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I might quibble with Augustine's language here--death is an evil, however much it is not to be feared by Christians. It is an enemy to be destroyed. (I Corinthians 15:26) Consequently, I think his statement "that death is not to be judged an evil which is the end of a good life; for death becomes evil only by the retribution which follows it" goes a step too far. Death even for a believer is a sign of a fallen world, and to be mourned for its existence as with every other evil.
But, his overall point is of course still a good one. At the end of the day, to put a Christian to death is no victory for the enemies of God at all. How contrary is this to the world's thinking? We have a natural tendency to think of individual death as the end, of wars as being won or lost based on casualty rates, and of the death penalty as the highest form of punishment that can be inflicted. Death in our natural line of thought is final and absolute. We overcome this natural tendency when as Christians we join Augustine (and Scripture) in holding to a higher truth--that death is no defeat if we have confidence in the certainty of a heavenly life after death. The eternal judgment of a righteous God for our rebellion against Him is infinitely more to be feared than the question of when we depart this life. "They, then, who are destined to die, need not be careful to inquire what death they are to die, but into what place death will usher them." But if the rebel has been reconciled, then the Christian can face death with confidence knowing that he will be ushered into heaven rather than hell. Because Christ has gone to hell in our place for our rebellion and opened the way to heaven through His death, our own deaths then become but a springboard into the victory He earned for us.
Chapter 12 and 13:
In these two chapters we are given a practical application of the proper Christian view of the body. As Christians, we are neither naturalists nor Gnostics. We believe that what happens to the body has no ultimate effect on the state of the soul before God and that there is a supernatural element to human nature that cannot be destroyed with the death of the body (and so are not naturalists); but we also believe that the soul and the body are bound up together and will eventually be reunited in the resurrection (and so are not Gnostics).
We see this in how Augustine discusses burial. Augustine was living at the end of the (pagan) era when it was believed that a failure to apply the proper funerary rites would keep the spirit from the afterlife. (The play Anitgone is based on this concept.) Christianity rejects this idea, understanding that the performance or non-performance of religious rituals over a person has no bearing on whether that person ends up in heaven or hell. To that end, desecrating the body of a believer, failing to bury it properly, and so on does us no harm. As Augustine says, it is not "an infliction to the dead, for they cannot feel the loss."
At the same time, we ourselves do not disdain the bodies of the dead but treat them with appropriate respect, "for the body is not an extraneous ornament or aid, but a part of man's very nature." And so whenever possible we respect the bodies of the dead as a part of the person temporarily in hiatus.
I suppose I should include a closing note about Augustine's use of the Apocrypha as an authoritative source, but I don't know that I'm the person to write such a note. Instead, I'll leave that to Jerome, who says that these books may be read "for the edification of the people, not to give authority to doctrines of the Church."
This is a sermon from last Fall that touches on a number of the same issues as I.9-13 of COG. As one example, "Personal Christian faith must exist to be real... but merely private religion is fake religion."