Did God, perchance, promise to Abraham in his seed the good works of the nations, so as to promise that which He Himself does, but did not promise the faith of the Gentiles, which men do for themselves; but so as to promise what He Himself does, did He foreknow that men would effect that faith? The apostle, indeed, does not speak thus, because God promised children to Abraham, who should follow the footsteps of his faith, as he very plainly says. But if He promised the works, and not the faith of the Gentiles certainly since they are not good works unless they are of faith (for “the righteous lives of faith,” and, “Whatsoever is not of faith is sin,” and, “Without faith it is impossible to please”), it is nevertheless in man’s power that God should fulfil what He has promised. For unless man should do what without the gift of God pertains to man, he will not cause God to give,—that is, unless man have faith of himself. God does not fulfil what He has promised, that works of righteousness should be given by God. And thus that God should be able to fulfil His promises is not in God’s power, but man’s. And if truth and piety do not forbid our believing this, let us believe with Abraham, that what He has promised He is able also to perform. But He promised children to Abraham; and this men cannot be unless they have faith, therefore He gives faith also.
Reproduced in full. Translation: Nicene and Post-Nicene Fathers, series 1, vol. 5 (Schaff, 1887), public domain (Public domain).