Romans 4:5

Abraham, before his vocation, was an idolater, according to Josephus; (Jewish Antiquities, lib. i. chap. viii.) according to some of the Rabbins, and as the Scripture itself seems to insinuate, Josue chap. xxiv; Isaias xliii; Wisdom x; Judith v. He did not then merit his vocation to the faith by his works. But when God had called him, and made him depart from his country, when he promised to him an innumerable posterity, Abraham believed in his promises, and it was reputed to him unto justice, that his faith and his justice were the pure gift of God. His faith was not a dead and speculative faith only, but an active faith, a faith animated by charity, as appears from the sequel of his life. (Calmet)