"Contrition" is defined explicitly by the Council of Trent (Sess. XIV, ch. iv de Contritione): "a sorrow of soul and a hatred of sin committed, with a firm purpose of not sinning in the future".
"Since it is requisite for the remission of sin that a man cast away entirely the liking for sin which implies a sort of continuity and solidity in his mind,
'" (Aquinas, In Lib. Sent. IV, dist. xvii; cf. Supplem. III, Q. i, a. 1).
I wonder what St Thomas explains. Is absolution the same as forgiveness? If the priest absolves the penitent, are the sins forgiven if there is no expression of contrition? We are taught that absolution takes away the guilt, but punishment must still be paid for its consequence.
This sorrow of soul is not merely speculative sorrow for wrong done, remorse of conscience, or a resolve to amend; it is a real pain and bitterness of soul together with a hatred and horror for sin committed; and this hatred for sin leads to the resolve to sin no more. The early Christian writers in speaking of the nature of contrition sometimes insist on the feeling of sorrow, sometimes on the detestation of the wrong committed (Augustine in P.L., XXXVII, 1901, 1902; Chrysostom, P.G., XLVII, 409, 410). Augustine includes both when writing: "Compunctus corde non solet dici nisi stimulus peccatorum in dolore pœ;nitendi" (P.L., Vol. VI of Augustine, col. 1440). Nearly all the medieval theologians hold that contrition is based principally on the detestation of sin. This detestation presupposes a knowledge of the heinousness of sin, and this knowledge begets sorrow and pain of soul. "A sin is committed by the consent, so it is blotted out by the dissent of the rational will; hence contrition is essentially sorrow. But it should be noted that sorrow has a twofold signification--dissent of the will and the consequent feeling; the former is of the essence of contrition, the latter is its effect" (Bonaventure, In Lib. Sent. IV, dist. xvi, Pt. I, art. 1). [See also St. Thomas Aquinas, Comment. in Lib. Sent. IV; Billuart (De Sac. Pœ;nit., Diss. iv, art. 1) seems to hold the opposite opinion.]
NECESSITY OF CONTRITION
Until the time of the Reformation no theologian ever thought of denying the necessity of contrition for the forgiveness of sin. But with the coming of Luther and his doctrine of justification by faith alone the absolute necessity of contrition was excluded as by a natural consequence. Leo X in the famous Bull "Exsurge" [Denzinger, no. 751 (635)] condemned the following Lutheran position: "By no means believe that you are forgiven on account of your contrition, but because of Christ's words, 'Whatsoever thou shalt loose', etc. On this account I say, that if you receive the priest's absolution, believe firmly that you are absolved, and truly absolved you will be, let the contrition be as it may." Luther could not deny that in every true conversion there was grief of soul, but he asserted that this was the result of the grace of God poured into the soul at the time of justification, etc. (for this discussion see Vacant, Dict. de théol. cath., s.v. Contrition.) Catholic writers have always taught the necessity of contrition for the forgiveness of sin, and they have insisted that such necessity arises (a) from the very nature of repentance as well as (b) from the positive command of God. (a) 'They point out that the sentence of Christ in Luke, xiii, 5, is final: "Except you do penance", etc., and from the Fathers they cite passages such as the following from Cyprian, "De Lapsis", no. 32: "Do penance in full, give proof of the sorrow that comes from a grieving and lamenting soul . . . they who do away with repentance for sin, close the door to satisfaction." Scholastic doctors laid down the satisfaction' principle, "No one can begin a new life who does not repent him of the old" (Bonaventure, In Lib. Sent. IV, dist. xvi, Pt. II, art. 1, Q. ii, also ex professo, ibid., Pt. I, art. I, Q. iii), and when asked the reason why, they point out the absolute incongruity of turning to God and clinging to sin, which is hostile to God's law. The Council of Trent, mindful of the tradition of the ages, defined (Sess. XlV. ch. iv de Contritione) that "contrition has always been necessary for obtaining forgiveness of sin". (b) The positive command of God is also clear in the premises. The Baptist sounded the note of preparation for the coming of the Messias: "Make straight his paths"; and, as a consequence "they went out to him and were baptized confessing their sins". The first preaching of Jesus is described in the words: "Do penance, for the kingdom of heaven is at hand"; and the Apostles, in their first sermons to the people, warn them to "do penance and be baptized for the remission of their sins" (Acts 2:38). The Fathers followed up with like exhortation (Clement in P.G., I, 341; Hermas iii P.G., II, 894; Tertullian in P.L., II).
In this contrition several things are to be observed, viz. the very substance of the act, the way of acting, its origin and its effect: in respect of which we find that contrition has been defined in various ways. For, as regards the substance of the act, we have the definition given above: and since the act of contrition is both an act of virtue, and a part of the sacrament of Penance, its nature as an act of virtue is explained in this definition by mentioning its genus, viz. "sorrow," its object by the words "for sins," and the act of choice which is necessary for an act of virtue, by the word "assumed": while, as a part of the sacrament, it is made manifest by pointing out its relation to the other parts, in the words "together with the purpose of confessing and of making satisfaction."
Contrition can be an interior desire and its effectiveness is made possible by the act
of reciting it. The Act is not merely expression of remorse but also a resolve NOT to sin again, to avoid the near occasions of sin, to do penance, and amend life (not to return to the previous state of committing sin). The Act of Contrition has been formulated precisely to be recited as part of the Sacrament of Penance, just as other forms of prayers have a formula; e.g., the Rosary cannot be effected by interiorly desiring it: the Rosary must be recited and contemplated, or else its benefits are for naught. Therefore, my opinion is that the Act of Contrition is necessary for confession. It is not optional and cannot be omitted.