Augustine of Hippo, On Grace and Free Will Chapter 18: Faith Without Good Works is Not Sufficient for Salvation

Unintelligent persons, however, with regard to the apostle’s statement: “We conclude that a man is justified by faith without the works of the law,” have thought him to mean that faith suffices to a man, even if he lead a bad life, and has no good works. Impossible is it that such a character should be deemed “a vessel of election” by the apostle, who, after declaring that “in Christ Jesus neither circumcision availeth anything, nor uncircumcision,” adds at once, “but faith which worketh by love.” It is such faith which severs God’s faithful from unclean demons,—for even these “believe and tremble,” as the Apostle James says; but they do not do well. Therefore they possess not the faith by which the just man lives,—the faith which works by love in such wise, that God recompenses it according to its works with eternal life. But inasmuch as we have even our good works from God, from whom likewise comes our faith and our love, therefore the selfsame great teacher of the Gentiles has designated “eternal life” itself as His gracious “gift.”