Don't believe then....
...but what the heck...
In the life of the body a man is sometimes sick, and unless he takes medicine, he will die. Even so in the spiritual life a man is sick on account of sin. For that reason he needs medicine so that he may be restored to health; and this grace is bestowed in the Sacrament of Penance.
~St. Thomas Aquinas
The minister to whom confession is made is the delegate of Christ, Who is the Judge of the living and the dead.
~St. Thomas Aquinas
Go to your confessor; open your heart to him; display to him all the recesses of your soul; take the advice that he will give you with the utmost humility and simplicity. For God, Who has an infinite love for obedience, frequently renders profitable the counsels we take from others, but especially from those who are the guides of our souls.
~St. Francis de Sales
Our Lord Himself I saw in . . . this venerable Sacrament . . . I felt as if my chains fell, as those of St. Peter at the touch of the Divine messenger. My God, what new scenes for my soul!
~St. Elizabeth Ann Seton
God desires from you the least degree of purity of conscience more than all the works you can perform.
~St. John of the Cross
John 20:21-23 is, for the most part, the main supporting verse for Confession. Also, 2 Corinthians 5:18.
"Since Christ entrusted to his apostles the ministry of reconciliation, 65 bishops who are their successors, and priests, the bishops' collaborators, continue to exercise this ministry. Indeed bishops and priests, by virtue of the sacrament of Holy Orders, have the power to forgive all sins 'in the name of the Father, and of the Son, and of the Holy Spirit.'"
-Catechism of the Catholic Church #1461
2 Cor 16-20 Consequently, from now on we regard no one according to the flesh; even if we once knew Christ according to the flesh, yet now we know him so no longer. So whoever is in Christ is a new creation: the old things have passed away; behold, new things have come. And all this is from God, who has reconciled us to himself through Christ and given us the ministry of reconciliation, namely, God was reconciling the world to himself in Christ, not counting their trespasses against them and entrusting to us the message of reconciliation. So we are ambassadors for Christ, as if God were appealing through us. We implore you on behalf of Christ, be reconciled to God.
In this passage, Paul is telling us about his ministry and the ministry of all the Apostles. He shows how and why he has power to forgive sin in the name of Christ. He also tells us the role of the priest.
"If we say we have no sin, we deceive ourselves, and the truth is not in us," (1 John 1:8). The Bible tells us that nothing unclean can enter heaven (Revelation 21:27) then that must mean that Jesus gave us a way to clean ourselves of sin after baptism and before our death.
*reconciliation with God by which the penitent recovers grace;
*reconciliation with the Church;
*remission of the eternal punishment incurred by mortal sins;
*remission, at least in part, of temporal punishments resulting from sin;
*peace and serenity of conscience, and spiritual consolation;
*an increase of spiritual strength for the Christian battle.
(Catechism of the Catholic Church 1496)