The Enchiridion by St. Augustine
Chapter 98.--Predestination to Eternal Life is Wholly of God's Free Grace.
And, moreover, who will be so foolish and blasphemous as to say that God cannot change the evil wills of men, whichever, whenever, and wheresoever He chooses, and direct them to what is good? But when He does this He does it of mercy; when He does it not, it is of justice that He does it not for |He hath mercy on whom He will have mercy, and whom He will He hardeneth.| And when the apostle said this, he was illustrating the grace of God, in connection with which he had just spoken of the twins in the womb of Rebecca, |who being not yet born, neither having done any good or evil that the purpose of God according to election might stand, not of works, but of Him that calleth, it was said unto her, The elder shall serve the younger.| And in reference to this matter he quotes another prophetic testimony: |Jacob have I loved, but Esau have I hated.| But perceiving how what he had said might affect those who could not penetrate by their understanding the depth of this grace: |What shall we say then?| he says: |Is there unrighteousness with God? God forbid.| For it seems unjust that, in the absence of any merit or demerit, from good or evil works, God should love the one and hate the other. Now, if the apostle had wished us to understand that there were future good works of the one, and evil works of the other, which of course God foreknew, he would never have said, |not of works,| but, |of future works,| and in that way would have solved the difficulty, or rather there would then have been no difficulty to solve. As it is, however, after answering, |God forbid;| that is, God forbid that there should be unrighteousness with God; he goes on to prove that there is no unrighteousness in God's doing this, and says: |For He saith to Moses, I will have mercy on whom I will have mercy, and I will have compassion on whom I will have compassion.| Now, who but a fool would think that God was unrighteous, either in inflicting penal justice on those who had earned it, or in extending mercy to the unworthy? Then he draws his conclusion: |So then it is not of him that willeth, nor of him that runneth, but of God that showeth mercy.| Thus both the twins were born children of wrath, not on account of any works of their own, but because they were bound in the fetters of that original condemnation which came through Adam. But He who said, |I will have mercy on whom I will have mercy,| loved Jacob of His undeserved grace, and hated Esau of His deserved judgment. And as this judgment was due to both, the former learnt from the case of the latter that the fact of the same punishment not falling upon himself gave him no room to glory in any merit of his own, but only in the riches of the divine grace; because |it is not of him that willeth, nor of him that runneth, but of God that showeth mercy.| And indeed the whole face, and, if I may use the expression, every lineament of the countenance of Scripture conveys by a very profound analogy this wholesome warning to every one who looks carefully into it, that he who glories should glory in the Lord.