Here is an excellent video clip that offers an explanation of why we must confess our sins to a priest. As we start the new year it may be worthwhile for us to consider more frequent confession.
""The whole power of the sacrament of Penance consists in restoring us to God's grace and joining us with him in an intimate friendship." Reconciliation with God is thus the purpose and effect of this sacrament. For those who receive the sacrament of Penance with contrite heart and religious disposition, reconciliation "is usually followed by peace and serenity of conscience with strong spiritual consolation." Indeed the sacrament of Reconciliation with God brings about a true "spiritual resurrection," restoration of the dignity and blessings of the life of the children of God, of which the most precious is friendship with God." (CCC 1468)