From Pope St. John Paul II’s Apostolic Exhortation Reconciliatio et Pænitentia (1984):
The books of the Old and New Testament provide us with the first and fundamental fact concerning the Lord’s mercy and forgiveness. In the Psalms and in the preaching of the prophets, the name merciful is perhaps the one most often given to the Lord, in contrast to the persistent cliche whereby the God of the Old Testament is presented above all as severe and vengeful. Thus in the Psalms there is a long sapiential passage drawing from the Exodus tradition, which recalls God’s kindly action in the midst of his people. This action, though represented in an anthropomorphic way, is perhaps one of the most eloquent Old Testament proclamations of the divine mercy. Suffice it to quote the verse: “Yet he, being compassionate, forgave their iniquity and did not destroy them; he restrained his anger often, and did not stir up all his wrath. He remembered that they were but flesh, a wind that passes and comes not again.”157
In the fullness of time the Son of God, coming as the lamb who takes away and bears upon himself the sin of the world158 appears as the one who has the power both to judge159 and to forgive sins,160 and who has come not to condemn but to forgive and save.161
Now this power to “forgive sins” Jesus confers through the Holy Spirit upon ordinary men, themselves subject to the snare of sin, namely his apostles: “Receive the Holy Spirit. Whose sins you shall forgive, they are forgiven; whose sins you shall retain, they are retained.”162 This is one of the most awe-inspiring innovations of the Gospel! He confers this power on the apostles also as something which they can transmit-as the church has understood it from the beginning-to their successors, charged by the same apostles with the mission and responsibility of continuing their work as proclaimers of the Gospel and ministers of Christ’s redemptive work.
Here there is seen in all its grandeur the figure of the minister of the sacrament of penance who by very ancient custom is called the confessor.
157 Ps 78(77):38f.
158 Cf Jn 1:29; Is 53:7-12.
159 Cf Jn 5:27.
160 Cf Mt 9:2-7; Lk 5:18-25; 7:47-49; Mk 2:3-12.
161 Cf Jn 3:17.
162 Jn 20:22; Mt 18:18; cf also, as regards Peter, Mt 16:19. Blessed Isaac of Stella in one of his talks emphasizes the full communion of Christ with the church in the forgiveness of sins: “The church can forgive nothing without Christ and Christ does not wish to forgive anything without the church. The church can forgive nothing except to a penitent, that is to say, to a person whom Christ has touched with his grace: Christ does not wish to consider anything forgiven in a person who despises the church”: Sermo 11 (“In Dominica II Post Epiphaniam,” 1): Patrologiae Cursus completus, Series Latina 194, 1729.
— Reconciliatio et Pænitentia 29