Chapter 19 — Part II: The Sacraments — Penance
Section 161. Conditions for Satisfaction — In satisfaction two things are particularly required: the one, that he who satisfies be in a state of grace, the friend of God, since works done without faith and charity cannot be acceptable to God; the other, that the works performed be such as are of their own nature painful or laborious. They are a compensation for past sins, and, to use the words of the holy martyr Cyprian, the redeemers, as it were, of past sins, and must, therefore, in some way be disagreeable.