The Catechism of St. Thomas Aquinas
The form of this Sacrament is the words of absolution which the priest speaks when he says: “I absolve thee” (“Ego te absolvo”). The minister of this Sacrament is the priest having authority to absolve, which is either ordinary or by commission of his superior. The effect of this Sacrament is absolution from sin.
Concerning this Sacrament is the error of the Novati, who say that any one who has sinned after having been baptized cannot receive pardon through the Sacrament of Penance. Against this are the words: “Be mindful therefore from whence thou art fallen; and do penance, and do the first works.”
27. 51. Thomas uses here the words: “quasi materia.” The “Roman Catechism” (“Penance,” 13) follows this teaching. “The faithful should be especially informed on the matter of this Sacrament. That it differs from the other Sacraments in that for them the matter is something, whether natural or artificial; the matter as it were (quasi-materia) of Penance is the acts of the penitent, i.e., contrition confession, and satisfaction. This has thus been defined by the Council of Trent. . . It is not because they are not the real matter that they are called by the Council the matter as it were, but because they are not of that sort of matter which is applied externally, such, for instance, as water in Baptism and chrism in Confirmation.”
28. “A knowledge of it [the form of Penance] will excite the faithful to receive the grace of this Sacrament with the greatest possible devotion. The form is: ‘I absolve thee,’ as may be inferred not only from the words: ‘Whatsoever you shall bind upon earth shall be bound also in heaven’ (Matt., xviii. 18), but also from the teaching of Christ Our Lord, handed down to us by the Apostles. . . . The minister of the Sacrament of Penance must be a priest possessing ordinary or delegated jurisdiction, as is evident in the law of the Church. Whoever performs this sacred duty must be invested not only with the powers of orders, but also with that of jurisdiction. We have greatest proof of this ministry in the words of Our Lord: ‘Whose sins you shall forgive, they are forgiven them; and whose sins you shall retain, they are retained’ John, xx. 23). These words were not addressed to all, but only to the Apostles, who are succeeded in this ministry by
priests” (“Roman Catechism,” loc. cit., 54).
29. Apoc., ii. 5.