Forgiveness of sins brings reconciliation with God, but also with the Church. Since ancient times the bishop, visible head of a particular Church, has thus rightfully been considered to be the one who principally has the power and ministry of reconciliation: he is the moderator of the penitential discipline. Priests, his collaborators, exercise it to the extent that they have received the commission either from their bishop (or religious superior) or the Pope, according to the law of the Church.
Source: Catechism of the Catholic Church (Vatican.va)