What is confession? Why do we confess our sins to a priest?
Confession is the sacrament that allows us to experience Christ's gift of mercy. In this sacrament we go before a priest and confess our mortal (serious sins). He counsels us, absolves us, and assigns a penance. This sacrament puzzles many who do not understand its root, purpose, and spiritual dynamic.
Why confess our sins to a man? It is what's best for us. First, Jesus gives His apostles the authority to forgives sins (see John 20:19-23) so we know that men can forgive sin provided they receive that authority from Christ. Confession forces us to develop humility because we have to admit our faults to another. This is an effective way of curbing ego and fostering contrition. It forces us to be accountable to God and ourselves. And perhaps the most profound part of the sacrament, we get to hear God's mercy and hear the words "I absolve you of your sins, go in peace."
For more on the Biblical and historical defense of the Sacrament of Penance (Confession) try these sites: