Some Fundamental Convictions
31. The truths mentioned above, powerfully and clearly confirmed by the synod and contained in the propositions, can be summarized in the following convictions of faith, to which are connected all the other affirmations of the Catholic doctrine on the sacrament of penance.
II. The second conviction concerns the function of the sacrament of penance for those who have recourse to it. According to the most ancient traditional idea, the sacrament is a kind of judicial action; but this takes place before a tribunal of mercy rather than of strict and rigorous justice, which is comparable to human tribunals only by analogy namely insofar as sinners reveal their sins and their condition as creatures subject to sin; they commit themselves to renouncing and combating sin; accept the punishment (sacramental penance) which the confessor imposes on them and receive absolution from him.
Whether as a tribunal of mercy or a place of spiritual healing, under both aspects the sacrament requires a knowledge of the sinner's heart in order to be able to judge and absolve, to cure and heal. Precisely for this reason the sacrament involves on the part of the penitent a sincere and complete confession of sins. This therefore has a raison d'etre not only inspired by ascetical purposes (as an exercise of humility and mortification), but one that is inherent in the very nature of the sacrament.