Nicene and Post-Nicene Fathers, Vol. II:
City of God: Chapter 4

Chapter 4.—Why Death, the Punishment of Sin, is Not Withheld from Those Who by the Grace of Regeneration are Absolved from Sin.

If, moreover, any one is solicitous about this point, how, if death be the very punishment of sin, they whose guilt is cancelled by grace do yet suffer death, this difficulty has already been handled and solved in our other work which we have written on the baptism of infants. 582   There it was said that the parting of soul and body was left, though its connection with sin was removed, for this reason, that if the immortality of the body followed immediately upon the sacrament of regeneration, faith itself would be thereby enervated.  For faith is then only faith when it waits in hope for what is not yet seen in substance.  And by the vigor and conflict of faith, at least in times past, was the fear of death overcome.  Specially was this conspicuous in the holy martyrs, who could have had no victory, no glory, to whom there could not even have been any conflict, if, after the layer of regeneration, saints could not suffer bodily death. p. 247 Who would not, then, in company with the infants presented for baptism, run to the grace of Christ, that so he might not be dismissed from the body?  And thus faith would not be tested with an unseen reward; and so would not even be faith, seeking and receiving an immediate recompense of its works.  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 thou sinnest, thou shall die;” now it is said to the martyr, “Die, that thou sin not.”  Then it was said, “If ye trangress the commandments, ye shall die;” now it is said, “If ye decline death, ye 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.

Footnotes

De Baptismo Parvulorum is the second half of the title of the book, de Peccatorum Meritis et Remissione.