Answer: Confession is a contrite acknowledgement of our sins to a priest, who is duly authorized by God (through the Church), in order to obtain forgiveness. This acknowledgement of our sins is an important and necessary part of the Holy Sacrament of Penance.
Even in the Old Law, a certain kind of confession was prescribed and connected with a sacrifice, called the sacrifice of Atonement: but the forgiveness of sins was effected only through faith in the coming Redeemer, towards whom the sacrifice pointed (Lev. 5:5-6; Num. 5:7; compare Mt. 3:6). In the new Law, Christ gave to the apostles and their successors power to forgive, and to retain sins (John 20:21-23), and in doing so made them judges. Without confession on the part of the sinner, a priest cannot act as a judge and do justice in regard to giving penalties and corrections. As the sinner is seldom able to make an act of perfect contrition, which is necessary to obtain the forgiveness of sins without confession, it was necessary that the most merciful Lord, through the means of confession to a priest, should provide in an easier manner for the common salvation of man.
God does not will to save fallen humankind without its cooperation, but by using human actions as means of redemption; first Jesus’ human actions, then those of the Church and her members. God’s forgiveness comes to the sinner in the sacrament of penance insofar as the priest acts not in his own person–he too is only human and in need of forgiveness—but in the person of Jesus. Because Jesus, who is God, really acts in and through the priest’s action, there is no more direct way of seeking God’s forgiveness than by using the sacrament of penance. The sacrament also has the advantage of providing a human encounter in which penitents know their sins are heard and absolved.
Confession is the best way for a person to acknowledge his sins and recognize the wickedness of such acts. Even Adam was obliged to acknowledge his sins, and in the same way Cain was asked by God about his brother’s murder, although God knew the sins of both. The desire to ease his conscience seems to have been born in man. King David says of his crime: “When I declared not my sin, my body wasted away through my groaning all day long” (Psalm 32:3), and in the Book of Proverbs it is said: “He who conceals his transgressions will not prosper, but he who confesses and forsakes them will obtain mercy” (28:13).