One of the great gifts of the Catholic Church is the power, given by Christ through the apostles, to forgive sin. When Christ forgave sin in front of the Pharisees they were scandalized. So too when the Church forgives through her priests in persona Christi people may fail to understand why another human being is necessary for reconciliation with God.
The first good reason for such an arrangement is simply this, because He willed it so. Just as Christ became Incarnate in order to save us, so He constructed the Church in such a way as to remain present to the world through our humanity. It is humbling to go to another sinner like ourselves in order to recover our peace with God. St. James writes, “Hence, declare your sins to one another, and pray for one another, that you may find healing.” (James 5:16)
It is clear from John 20 quoted above that Christ is speaking of a power not given to all, otherwise any Christian could hold bound another’s sin and prevent them from finding peace and forgiveness. The history of the Church shows very early that if one wanted to repent of serious sin after baptism one needed to go to the bishop. Early Christians believed as we do that when one member of the Body of Christ had fallen out of communion with the rest of the Body, thus renouncing in some way their connection to the Body, a healing was necessary through the instrumentation of the Bishop. As early as 70 AD, this was recorded in a reliable document called the Didache (Teaching of the Twelve Apostles), "In church confess your sins, and do not come to your prayer with a guilt conscience. Such is the Way of Life...On the Lord's own day, assemble in common to break bread and offer thanks; but first confess your sins, so that your sacrifice may be pure."
The Sacramental Rite of Reconciliation is composed of five steps:
1. Examination of Conscience
We ask the Holy Spirit to help us know our sins and give us true contrition for them
2. Confession of Sin
We tell our sins to the priest
3. Penance and Counsel
The priest gives us any pertinent advice and some act of penance (a prayer or deed)
4. Act of Contrition and Absolution
After a prayer of sorrow the priest gives us Christ’s absolution
We fulfill the penance given by the priest