Explanation of Confession
Confession is pretty well-known as a mostly Catholic practice, and there are a lot of people who don’t' agree with it. It is one of the seven sacraments, those signs and actions of the church which impart grace, so it is very important to both understand and frequently use. It is one of the most powerful ways by which we can receive grace to live a life more in accordance with God's will for us.
Baptism wipes away all sins, both original sin and actual sin. If a person is baptized as a child, then they have committed no personal sins, so only original sin is wiped away, and they are filled with grace. If a person is baptized when they are older, they may have committed sins themselves. At baptism, both original sin and all these personal sins are wiped away. However, baptism doesn't stop us from sinning in the future, and for the most part everyone does sin at some point after their baptism. Thus God instituted the sacrament of Penance in order to forgive these sins committed after Baptism.
During confession the priest assigns a small penance to be performed after confession. This usually consists of saying a few prayers or doing some small act of kindness. These are meant to be small tokens of repentance. By offering this prayer or sacrifice, the person makes some small reparation for the harm they have done to their soul and to their relationship with God. It is also a reminder to try to live a better life and avoid that sin in the future.
Why have confession?
The sacrament of Penance involves confessing one's sins to a priest, who acts as God's minister and representative. Since sin is an offense against God, only He can forgive sin, but He has chosen to use priests as an earthly representative of His mercy and forgiveness. The sacrament of Penance is both humbling and uplifting. It is humbling because it requires confessing ones faults and sins to another human being. Even though this other person is a representative of Christ and keeps your sins a secret, there is something humbling and sometimes difficult with acknowledging your sins out loud and to another person. This is even more the case when perhaps the sin is private or something of which we are ashamed. By saying it out loud, we are forced to acknowledge it to ourselves. However, it is also uplifting because we are assured of forgiveness from God. When the priest pronounces the words of absolution, we have God's assurance that He is forgiving us through the priest. There is no conditional forgiveness. Priests are given the authority to forgive or not in the name of Christ, and whatever their decision is also upheld in Heaven. It also can lift a psychological burden off a person. Many times the guilt of sin can weigh on a person and the revealing of that sin in confession and its forgiveness can lift a burden and make that person much relieved.
There is an obligation for every Catholic to go to confession at least once a year, particularly if he or she is guilty of a mortal sin. Of course going to confession more often is always encouraged. Even if a person has not committed any mortal sins, he or she can still confess venial sins. By acknowledging these failings, grace will be received to continue to combat them in the future. Many of the saints have advocated for frequent confession, because this is one of the best ways to gain grace.
In the Bible
Many Protestants believe that it is sufficient to confess one's sins to God and that confession to a priest is not necessary. As Catholics see it, they are indeed confessing to God, but also the priest who is God's representative. “Receive the Holy Spirit. If you forgive the sins of any, they are forgiven them; if you retain the sins of any, they are retained.” - John 20: 22 – 23 In this passage from the gospel of John, Jesus speaks to His disciples shortly after the Resurrection. He tells them to use the gift of the Holy Spirit to forgive sins. This is one place in the scriptures in which Jesus speaks of confessing to another person, not straight to God. He speaks of the apostles forgiving people in the name of God, and that forgiveness being equated with the forgiveness of God. He clearly is speaking of human agents in God forgiving sins.
Seal of Confession
One of the very reassuring parts of confession is that the priest is bound to never reveal sins that he hears while administering the sacrament. If he does so, he incurs an automatic excommunication. This is very reassuring to those who might not, for whatever reason, want their sins made public. Whatever is said during confession will remain there and will never be revealed by the priest. This is a great comfort to many, and it also requires much sacrifice and watchfulness on the part of priests. They must be careful to never reveal anything inadvertently and if they are pressured by civil authorities to reveal something, they cannot. There have been priests who have died martyrs because they refused to reveal what someone confessed, and they preferred to die rather than break this seal of confession.