Why do Catholics confess their sins to a priest and not to God?
Catholics always confess their sins to God. They do it directly (they are taught to make an act of contrition every evening and immediately after serious sin) as well as through His priests (in the Sacrament of Auricular Confession) because that is what God requires, as is clearly taught in Scripture. In James 5: 13-16, James makes clear that the sins of the sick are forgiven in the sacrament of anointing. He specifies that the presbyters (priests) must be called. They obviously had a power the ordinary Christian did not: the power to forgive sins. Otherwise, why didn’t James simply ask ordinary, fellow Christians to pray over the sick as is the case in numerous other passages. In 2 Cor 5: 17-20, Christ’s work of reconciliation can only mean that the Apostles (and by inference their successors) share in the ministry of Christ and forgive sins in His name. St Paul certainly exercised the power of binding and loosing from sin (Jn 20: 19-23) in the case of the incestuous Corinthian in 1 Cor 5: 3 where we find him saying, "I have already judged him that hath done so"; and in 2 Cor 2: 10 he justifies his forgiveness of the repentant man by saying, "If I have pardoned anything, I have done it in the person of Christ." Also, from Satan’s point of view, what empties the sinner of more pride? To confess one’s sins to God in the relative comfort zone of one’s own heart; or to confess to God through another human being who acts in the person of Christ? Until the Protestant Reformation all Christians went to Confession with a priest. In the 4th century we find St Ambrose defending the Sacrament of Confession by saying that if a man can forgive sin by baptising, he claims nothing greater when he claims the power to forgive sin through the Sacrament of Confession. In Jn 20: 19-23 the Apostles are to continue the mission of Christ which is, in essence, THE FORGIVENESS OF SINS. Clearly, Christ gave His disciples the power to forgive sin. This power was intended to be passed on, since Christ knew people would sin until the end of time. Early Church history confirms that Christians believed this power was passed on to the Apostles. Please note, the priest hearing the confession does not redeem the penitent, he is simply an accredited agent of the one Mediator Jesus Christ. That one Mediator has commanded us to confess our sins to the priests of the Church that He founded. Jesus knows our human nature better than we do. He provided sacramental confession to give us: humility, the certainty of forgiveness, spiritual direction, and help to overcome self-deception and rationalisation in matters of sin.
See also Jurgens, The Faith of the Early Fathers, # 493, 553, 602, 637, 855a
* Please note that this text should be read in the context of the whole work and in recognition of the appropriate paragraphs of the Catechism of the Catholic Church highlighted in the index.