Augustine of Hippo, On Rebuke and Grace Chapter 36: God Not Only Foreknows that Men Will Be Good, But Himself Makes Them So

It is He Himself, therefore, that makes those men good, to do good works. For He did not promise them to Abraham because He foreknew that of themselves they would be good. For if this were the case, what He promised was not His, but theirs. But it was not thus that Abraham believed, but “he was not weak in faith, giving glory to God;” and “most fully believing that what He has promised He is able also to perform.” He does not say, “What He foreknew, He is able to promise;” nor “What He foretold, He is able to manifest;” nor “What He promised, He is able to foreknow:” but “What He promised, He is able also to do.” It is He, therefore, who makes them to persevere in good, who makes them good. But they who fall and perish have never been in the number of the predestinated. Although, then, the apostle might be speaking of all persons regenerated and living piously when he said, “Who art thou that judgest another man’s servant? To his own master he standeth or falleth;” yet he at once had regard to the predestinated, and said, “But he shall stand;” and that they might not arrogate this to themselves, he says, “For God is able to make him stand.” It is He Himself, therefore, that gives perseverance, who is able to establish those who stand, so that they may stand fast with the greatest perseverance; or to restore those who have fallen, for “the Lord setteth up those who are broken down.”