1. The Catholic Church definitively teaches that the sacrament of penance is necessary for those who commit mortal sin after baptism.

2. Still, in order to be forgiven, is it not sufficient to be genuinely sorry for sin out of love of God, even apart from the sacrament? Trent “teaches that, although it does sometimes happen that this contrition is made perfect through charity and reconciles man to God before the sacrament is actually received, nevertheless the reconciliation must not be attributed to contrition exclusive of the desire for the sacrament included in the contrition.” In other words, some sort of desire for the sacrament is necessary for perfect contrition.

3. The essential parts of the sacrament are the acts of contrition, confession, and satisfaction on the part of the penitent and the act of absolution on the part of the minister. Absolution is the wiping out of sin; the bonds which held the sinner fall away. “The complete effect of this sacrament, so far as its full efficaciousness is concerned, is reconciliation with God, which, in devout men who receive the sacrament with devotion, is sometimes followed by peace and serenity of conscience joined to a great consolation of soul.”

4. Although the sacrament of penance is similar to baptism in overcoming sin and conferring divine life, it is not simply a repetition of baptism. These sacraments differ in important ways.

Conversion, contrition, repentance, turning toward God--all the same thing--is not once and for all. If we sin mortally after baptism, a new and radical conversion is again needed. But even if we do not sin mortally, venial sins detract from friendship with God. Thus, continuing repentance is essential in every Christian life (see Rom 6.12-14; Eph 4.20-24; Col 3.1-17).

God desires the reconciliation of sinners. He does not wish any soul to be lost (see Mt 18.10-14; Lk 15.3-7). If we are faithful to Jesus, we will enjoy glory with him; if we are unfaithful, he will disown us, for he is faithful even when we are unfaithful. He keeps his promises even when we do not; he constantly seeks our free surrender to his love (see 2 Tm 2.11-13). For this reason, Jesus gave his Church the power to bind and loose. The Church from the beginning used this power to rescue sinners (see Mt 16.15-19; 18.15-18; Jn 20.22-23; 1 Cor 5.1-5; 2 Cor 2.5-11).

5. Repentance for grave sin committed after baptism requires not only that one give up one’s sins and detest them (this is required also by baptism) but that one make, or at least in some way desire to make, a sacramental confession and receive the absolution of a priest. Moreover, the newly baptized person is freed by baptism not only from the guilt of sin but from all temporal punishment due to it; but those who receive forgiveness in the sacrament of penance are still obliged to do something by way of satisfaction for their sins.

6. The requirement that grave sins be confessed gives this sacrament an essentially judicial character. The sinner stands trial, as it were--although pardon is guaranteed, provided the right dispositions are present. The unpleasant act of confessing, together with the need to do penance to satisfy for sin, make the sacrament of penance an arduous way to renew the integrity of baptism.

To remit sins subsequent to baptism, it is not sufficient simply to recall one’s baptism. The requirement that Christians confess their sins to a priest is clearly taught by many Fathers of the Church: St. Cyprian of Carthage, Aphraates the Persian Sage, St. John Chrysostom, St. Ambrose, St. Augustine, St. Cyril of Alexandria, and St. Leo the Great.

Worthy reception of the Eucharist requires that those who have committed a mortal sin receive sacramental penance before receiving Holy Communion, unless they do not have access to a confessor and must celebrate Mass or participate in the Eucharist. A priest who celebrates Mass without having confessed should confess as soon as he can.

During his life on earth, Jesus often showed his power to forgive sins (see Lk 5.18-26; 7.36-50). When he handed over his saving work to the apostles after his resurrection, he gave them the sacrament of penance as a means by which they might apply the merit of his death for the forgiveness of sin committed after baptism.

The Catholic Church definitively teaches that Jesus instituted the sacrament of penance when he said: “Receive the Holy Spirit. If you forgive the sins of any, they are forgiven; if you retain the sins of any, they are retained” (Jn 20.22-23). Some deny that Jesus instituted the sacrament of penance by this conferral of authority. However, the binding and loosing referred to in the passage quoted is involved in no other centrally important act of the Church--certainly not in baptism, where no judicial act is required.

7. Still, why is it not enough to seek reconciliation with God in one’s heart? The answer lies in the ecclesial aspect of sin and the sacrament of penance mentioned by Vatican II: “Those who approach the sacrament of penance obtain pardon from the mercy of God for offenses committed against him. They are at the same time reconciled with the Church, which they have wounded by their sins, and which by charity, example, and prayer seeks their conversion” (LG 11). Christians are not united to God in a purely spiritual way and as isolated individuals. Union with him comes about in the Church, through socially structured, visible actions. Sin, however, disrupts one’s relationship with the Church, as well as with God. Reconciliation therefore requires that the sinner be restored to God by being humanly reconciled with the Church. The sacrament of penance’s human encounter and judicial aspect are indispensable to this human reconciliation.

The ecclesial significance of mortal sin was discussed earlier. Corresponding to the ecclesial significance of sin is the ecclesial dimension of the sacrament of penance. The ancient Gelasian Sacramentary provides a formula for reconciliation which makes clear this aspect of the sacrament. The bishop prays: “Bestow, we beseech you, O Lord, on this your servant, fruit worthy of penance, that by obtaining pardon for the sins he has admitted, he may be restored unharmed to your holy Church, from whose wholeness he has strayed by sinning.”

The Introduction to the new rite of penance expands upon the ecclesial aspect of this sacrament: “‘By the hidden and loving mystery of God’s design men are joined together in the bonds of supernatural solidarity, so much so that the sin of one harms the others just as the holiness of one benefits the others’ [reference omitted]. Penance always entails reconciliation with our brothers and sisters who are always harmed by our sins. In fact, men frequently join together to commit injustice. It is thus only fitting that they should help each other in doing penance so that they who are freed from sin by the grace of Christ may work with all men of good will for justice and peace in the world.” By mortal sin, one is unfaithful not only to God but to the Church. That is why the mortal sinner is excluded from Holy Communion. The absolution of the sacrament of penance readmits the sinner into perfect communion with the Church and by this very fact brings the sinner back to friendship with God.

The Church definitively teaches that to obtain remission of sins, confession of each and every mortal sin found during diligent self-examination is required by divine law. Also, the Church definitively insists that such confession is not impossible and that the requirement of it is no mere human tradition.

The requirement of integral confession of sins in kind and number is implicit in the character of absolution, which is a judicial act in which the Church’s power to bind and loose is exercised by pardoning the sinner. The judgment cannot be rendered without a statement of the case. Nor can appropriate penances be imposed if sins are not manifested. All mortal sins, including the circumstances which alter their kind and seriousness, must be confessed. Venial sins need not but may be confessed. Confessing one’s sins seems burdensome but the burden is lightened for those who receive the sacrament worthily by the great benefits received with absolution and also by confidence in the secrecy of the confessional.

In any human interpersonal relationship, a sincere and open admission of wrongdoing, by its very difficulty for the one who makes it, goes some way toward making up for the wrong done; so in the sacrament of penance, honest and complete confession of sin by one truly contrite is itself a penitential act of considerable value. There is a tendency to evade the requirement of detailed, integral confession of sins. The likelihood that self-deception is involved should not be overlooked. One generally not only is embarrassed to speak openly of one’s sins, but also is reluctant to make a perfectly clean break with them. If integral confession were not required, many of us would limit and so corrupt our contrition, thus settling for a feeling of repentance without its reality.

--Source: Christian Moral Principles. Chapter 32: Penance, Anointing, and the Life of Self-Denial