But now, by the greater and more admirable grace of the Saviour, the punishment of sin is turned to the service of righteousness. For then it was proclaimed to man, “If you sin, you shall die;” now it is said to the martyr, “Die, that you sin not.” Then it was said, “If you trangress the commandments, you shall die;” now it is said, “If you decline death, you transgress the commandment.” That which was formerly set as an object of terror, that men might not sin, is now to be undergone if we would not sin. Thus, by the unutterable mercy of God, even the very punishment of wickedness has become the armor of virtue, and the penalty of the sinner becomes the reward of the righteous. For then death was incurred by sinning, now righteousness is fulfilled by dying. In the case of the holy martyrs it is so; for to them the persecutor proposes the alternative, apostasy or death. For the righteous prefer by believing to suffer what the first transgressors suffered by not believing. For unless they had sinned, they would not have died; but the martyrs sin if they do not die. The one died because they sinned, the others do not sin because they die. By the guilt of the first, punishment was incurred; by the punishment of the second, guilt is prevented. Not that death, which was before an evil, has become something good, but only that God has granted to faith this grace, that death, which is the admitted opposite to life, should become the instrument by which life is reached.
Augustine, City of God, Book XIII, Chapter 5