Our brother Nick Nowalk recently made me aware of the following penetrating statement from Barrett on what Paul's gospel repudiates.
It has frequently been asked why Paul speaks often of faith, seldom of repentance. It cannot be said that he did not know the meaning of repentance. . . . But for Paul faith is not essentially a matter of turning away from a bad way of life; it is equally, and at a deeper level, a turning away from a good life in which one depends on one's own achievement, one's own works done in obedience to the moral law. . . . In order to believe man repudiates not only his bad morals but his good morals. Repentance is a term that would not adequately cover this.
--C. K. Barrett, Paul: An Introduction to His Thought (Westminster John Knox 1994), 102