God's Word promises "If we confess our sins, He is faithful and just to forgive us and cleanse us from all unrighteousness" (1 John 1:9). The faithful are to bring their sins to God in repentance, and through appropriate preparation receive cleansing and forgiveness.
The early Christians would stand and confess their sins to God in the presence of the whole congregation. Jesus encouraged His followers to walk in the light together, to confront problems corporately, to "tell it to the church" (Matt18:17). Thus James writes, "Confess your trespasses to one another" (James 5:16). But as time went on and the Church grew in numbers, strangers came to visit and public confession became more difficult. Out of mercy, priests began to witness confessions of sin privately on behalf of the Church (also see Confession by Fr Dimitri Tsakas).
Christ, giving His disciples the authority to forgive sin, said, "If you forgive the sins of any, they are forgiven them; if you retain the sins of any, they are retained" (John 20:23; cf. Matt 16:19, 18:17-19). From the beginning, Christians understood that the grace of ordination endowed the shepherd of the flock with the discernment and compassion to speak the words of remission, on behalf of Christ, regarding the sins of those who confess and turn from sin. For God has promised the removing of sin from us "as far as the east is from the west" (Ps 103:12). St John Chrysostom says, "The priests decree below, God confirms above, and the Master agrees with the opinion of His slaves".
"You did not choose Me", Jesus told the Twelve, "but I chose you and appointed you." (John 15:16). To these same disciples Jesus promised, "It is not you who speak but the Holy Spirit" (Mark 13:11). Whom God calls, He equips. Paul writes to Timothy, "Stir up the gift of God which is in you through the laying on of my hands" (2 Tim 1:6). It is the grace of the Holy Spirit which enables the priest to serve God and the people. Priests are only the visible instrument of God's mercy at the performance of the Mystery, which is performed invisibly through them by God Himself. It is God (the Holy Triune) who forgives our sins.
Thus the Church has encouraged her faithful: If you know you have committed a specific sin, do not hide it but confess it before coming to the Holy Eucharist. St Paul wrote, "Let a man examine himself, and so let him eat of the bread and drink of the cup" (1 Cor 11:28), and "If we would judge ourselves, we would not be judged" (1 Cor 11:31).
King David learned a lesson regarding his sin which is recorded for our benefit. For about a year, he had hidden his sins of adultery with Bathsheda and the murder of her husband (2 Sam 11:1-12:13). Then, confronted by Nathan the prophet, David repented from his heart and confessed his sin in a Psalm which is used for general confession to this day (Psalm 51). The joy of salvation was restored to him.
People ask, "Can't I confess to God privately?" Certainly, though there is no clear biblical basis for it. Even general confession occurs in the Church. In His mercy, God provides the sacrament of confession (more properly called the Sacrament of Repentance) to give us deliverance from sin and from what psychologists call denial. It is easy to pray in isolation, yet never come clean. It is far more effective to confess aloud to God before a priest, and benefit from his guidance and help.
It is essential to remember that the remission of sins in the Sacrament is an act of mercy. It is given for our spiritual profit, "for edification, and not for destruction" (2 Cor 10:8).
Thus we come before the holy icon of Christ, to whom we confess, and are guided by the priest, our spiritual father, in a cleansing inventory of our lives. When we tell God all, naming our sins and failures, we hear those glorious words of freedom which announces Christ's promise of forgiveness of all our sins. We resolve to "go and sin no more" (John 8:11).