104. Consequently, God would have willed to preserve even the first man in that state of salvation in which he was created and would have brought him in due season, after the begetting of children, to a better state without the intervention of death-where he not only would have been unable to sin, but would not have had even the will to sin-if he had foreknown that man would have had a steadfast will to continue without sin, as he had been created to do. But since he did foreknow that man would make bad use of his free will-that is, that he would sin-God prearranged his own purpose so that he could do good to man, even in man's doing evil, and so that the good will of the Omnipotent should be nullified by the bad will of men, but should nonetheless be fulfilled.
105. Thus it was fitting that man should be created, in the first place, so that he could will both good and evil-not without reward, if he willed the good; not without punishment, if he willed the evil. But in the future life he will not have the power to will evil; and yet this will not thereby restrict his free will. Indeed, his will will be much freer, because he will then have no power whatever to serve sin. For we surely ought not to find fault with such a will, nor say it is no will, or that it is not rightly called free, when we so desire happiness that we not only are unwilling to be miserable, but have no power whatsoever to will it.
And, just as in our present state, our soul is unable to will unhappiness for ourselves, so then it will be forever unable to will iniquity. But the ordered course of God's plan was not to be passed by, wherein he willed to show how good the rational creature is that is able not to sin, although one unable to sin is better.  So, too, it was an inferior order of immortality-but yet it was immortality-in which man was capable of not dying, even if the higher order which is to be is one in which man will be incapable of dying. 
106. Human nature lost the former kind of immortality through the misuse of free will. It is to receive the latter through grace-though it was to have obtained it through merit, if it had not sinned. Not even then, however, could there have been any merit without grace. For although sin had its origin in free will alone, still free will would not have been sufficient to maintain justice, save as divine aid had been afforded man, in the gift of participation in the immutable good. Thus, for example, the power to die when he wills it is in a man's own hands-since there is no one who could not kill himself by not eating (not to mention other means). But the bare will is not sufficient for maintaining life, if the aids of food and other means of preservation are lacking.
Similarly, man in paradise was capable of self-destruction by abandoning justice by an act of will; yet if the life of justice was to be maintained, his will alone would not have sufficed, unless He who made him had given him aid. But, after the Fall, God's mercy was even more abundant, for then the will itself had to be freed from the bondage in which sin and death are the masters. There is no way at all by which it can be freed by itself, but only through God's grace, which is made effectual in the faith of Christ. Thus, as it is written, even the will by which "the will itself is prepared by the Lord"  so that we may receive the other gifts of God through which we come to the Gift eternal-this too comes from God.
107. Accordingly, even the life eternal, which is surely the wages of good works, is called a gift of God by the apostle. "For the wages of sin," he says, "is death; but the gift of God is eternal life in Christ Jesus our Lord."  Now, wages for military service are paid as a just debit, not as a gift. Hence, he said "the wages of sin is death," to show that death was not an unmerited pun ishment for sin but a just debit. But a gift, unless it be gratuitous, is not grace. We are, therefore, to understand that even man's merited goods are gifts from God, and when life eternal is given through them, what else do we have but "grace upon grace returned"  ?
Man was, therefore, made upright, and in such a fashion that he could either continue in that uprightness-though not without divine aid-or become perverted by his own choice. Whichever of these two man had chosen, God's will would be done, either by man or at least concerning him. Wherefore, since man chose to do his own will instead of God's, God's will concerning him was done; for, from the same mass of perdition that flowed out of that common source, God maketh "one vessel for honorable, another for ignoble use"  ; the ones for honorable use through his mercy, the ones for ignoble use through his judgment; lest anyone glory in man, or-what is the same thing-in himself.
108. Now, we could not be redeemed, even through "the one Mediator between God and man, Man himself, Christ Jesus,"  if he were not also God. For when Adam was made-being made an upright man-there was no need for a mediator. Once sin, however, had widely separated the human race from God, it was necessary for a mediator, who alone was born, lived, and was put to death without sin, to reconcile us to God, and provide even for our bodies a resurrection to life eternal-and all this in order that man's pride might be exposed and healed through God's humility. Thus it might be shown man how far he had departed from God, when by the incarnate God he is recalled to God; that man in his contumacy might be furnished an example of obedience by the God-Man; that the fount of grace might be opened up; that even the resurrection of the body-itself promised to the redeemed-might be previewed in the resurrection of the Redeemer himself; that the devil might be vanquished by that very nature he was rejoicing over having deceived-all this, however, without giving man ground for glory in himself, lest pride spring up anew. And if there are other advantages accruing from so great a mystery of the Mediator, which those who profit from them can see or testify-even if they cannot be described-let them be added to this list.
 Another example of Augustine's wordplay. Man's original capacities included both the power not to sin and the power to sin (posse non peccare et posse peccare). In Adam's original sin, man lost the posse non peccare (the power not to sin) and retained the posse peccare (the power to sin)-which he continues to exercise. In the fulfillment of grace, man will have the posse peccare taken away and receive the highest of all, the power not to be able to sin, non posse peccare. Cf. On Correction and Grace XXXIII.
 Again, a wordplay between posset non mori and non possit mori.