[Jesus] said to them again, ‘Peace be with you. As the Father has sent me, so I send you.’ And when he had said this, he breathed on them and said to them, ‘Receive the holy Spirit. Whose sins you forgive are forgiven them, and whose sins you retain are retained.  1 Jn 20:21-23

Those who approach the sacrament of Penance obtain pardon from God’s mercy for the offense committed against him, and are, at the same time, reconciled with the Church which they have wounded by their sins and which by charity, by example, and by prayer labors for their conversion.
Catechism of the Catholic Church, 1422