Catechesis: Repentance

Yet the confidence was placed in our work of satisfaction. If the satisfaction could be perfect, confidence would be placed in it entirely. Neither faith nor Christ would be necessary. But such confidence was impossible. Even though someone had done penance that way for a hundred years, he would still not know whether he had finished his penance. That meant doing penance forever and never coming to repentance.—SA III, III, 23