The Sacrament of Reconciliation is for our spiritual healing. According to the Gospels, after the Resurrection, Jesus appeared to the apostles, breathed on them, and said, “Receive the Holy Spirit whose sins you shall forgive, they are forgiven them; whose sins you shall retain, they are retained.” (John 20:22-23) The reason for this sacrament is to heal our spiritual wounds, which we call sin.
Catholics must confess all known mortal sins to a priest. By doing this, we put ourselves in the state of grace necessary to receive the Holy Eucharist.
Confessing sins to a priest is not as difficult as people think. Most people tell sensitive, delicate and confidential information to their doctor or lawyer, so why not a priest? The priest is bound by the most absolute secrecy and confidentiality known to humankind. Not even the Pope can get the priest to reveal what was said in the confessional.