Here is St. Augustine in his own words:
*Predestination and the Justice of God
- Furthermore, who would be so impiously foolish as to say that God cannot turn the evil wills of men–as he willeth, when he willeth, and where he willeth–toward the good? But, when he acteth, he acteth through mercy; when he doth not act, it is through justice. For, "he hath mercy on whom he willeth; and whom he willeth, he hardeneth."205
Now when the apostle said this, he was commending grace, of which he had just spoken in connection with the twin children in Rebecca’s womb: "Before they had yet been born, or had done anything good or bad, in order that the electing purpose of God might continue–not through works but through the divine calling–it was said of them, ‘The elder shall serve the younger.’ "206 Accordingly, he refers to another prophetic witness, where it is written, "Jacob I loved, but Esau have I hated."207 Then, realizing how what he said could disturb those whose understanding could not penetrate to this depth of grace, he adds: "What therefore shall we say to this? Is there unrighteousness in God? God forbid!"208 Yet it does seem unfair that, without any merit derived from good works or bad, God should love the one and hate the other. Now, if the apostle had wished us to understand that there were future good deeds of the one, and evil deeds of the other–which God, of course, foreknew–he would never have said “not of good works” but rather “of future works.” Thus he would have solved the difficulty; or, rather, he would have left no difficulty to be solved. As it is, however, when he went on to exclaim, “God forbid!”–that is, “God forbid that there should be unfairness in God”–he proceeds immediately to add (to prove that no unfairness in God is involved here), "For he says to Moses, ‘I will have mercy on whom I will have mercy, and I will show pity to whom I will show pity.’"209 Now, who but a fool would think God unfair either when he imposes penal judgment on the deserving or when he shows mercy to the undeserving? Finally, the apostle concludes and says, "Therefore, it is not a question of him who wills nor of him who runs but of God’s showing mercy."210
Thus, both the twins were "by nature children of wrath,"211 not because of any works of their own, but because they were both bound in the fetters of damnation originally forged by Adam. But He who said, “I will have mercy on whom I will have mercy,” loved Jacob in unmerited mercy, yet hated Esau with merited justice. Since this judgment of wrath was due them both, the former learned from what happened to the other that the fact that he had not, with equal merit, incurred the same penalty gave him no ground to boast of his own distinctive merits–but, instead, that he should glory in the abundance of divine grace, because "it is not a question of him who wills nor of him who runs, but of God’s showing mercy."212 And, indeed, the whole visage of Scripture and, if I may speak so, the lineaments of its countenance, are found to exhibit a mystery, most profound and salutary, to admonish all who carefully look thereupon "that he who glories, should glory in the Lord."213
- Now, after the apostle had commended God’s mercy in saying, “So then, there is no question of him who wills nor of him who runs, but of God’s showing mercy,” next in order he intends to speak also of his judgment–for where his mercy is not shown, it is not unfairness but justice. For with God there is no injustice. Thus, he immediately added, "For the Scripture says to Pharaoh, 'For this very purpose I raised you up, that I may show through you my power, and that my name may be proclaimed in all the earth."214 Then, having said this, he draws a conclusion that looks both ways, that is, toward mercy and toward judgment: “Therefore,” he says, “he hath mercy on whom he willeth, and whom he willeth he hardeneth.” He showeth mercy out of his great goodness; he hardeneth out of no unfairness at all. In this way, neither does he who is saved have a basis for glorying in any merit of his own; nor does the man who is damned have a basis for complaining of anything except what he has fully merited. For grace alone separates the redeemed from the lost, all having been mingled together in the one mass of perdition, arising from a common cause which leads back to their common origin. But if any man hears this in such a way as to say: "Why then does he find fault? For who resists his will?"215 --as if to make it seem that man should not therefore be blamed for being evil because God “hath mercy on whom he willeth and whom he willeth he hardeneth”–God forbid that we should be ashamed to give the same reply as we see the apostle giving: "O man, who are you to reply to God? Does the molded object say to the molder, ‘Why have you made me like this?’ Or is not the potter master of his clay, to make from the same mass one vessel for honorable, another for ignoble, use?"216
There are some stupid men who think that in this part of the argument the apostle had no answer to give; and, for lack of a reasonable rejoinder, simply rebuked the audacity of his gainsayer. But what he said–“O man, who are you?”–has actually great weight and in an argument like this recalls man, in a single word, to consider the limits of his capacity and, at the same time, supplies an important explanation.