From John Paul II's Reconciliation and Penance (n. 26):
He [man] seems to refuse instinctively and often irresistibly anything that is penance in the sense of a sacrifice accepted and carried out for the correction of sin. In this regard I would like to emphasize that the church's penitential discipline, even though it has been mitigated for some time, cannot be abandoned without grave harm both to the interior life of individual Christians and of the ecclesial community and also to their capacity for missionary influence.