Priests can forgive our sins because Jesus has given them that authority through the grace of Holy Orders. With that power, priests can hear and forgive our sins by acting through Christ.
Jesus gave the Church the Sacrament of Reconciliation, also known as Penance or Confession, to allow us to have an intimate conversation with our God through the priest. We confess our sins to a priest, who is the minister of the sacrament, because he stands “in Persona Christi,” meaning that he is in the person of Christ.
It is through the Sacrament of Reconciliation that the stains of even our grave, mortal sins are actually removed from our souls and we are given new life. While we may talk to God in prayer to ask for forgiveness for our venial sins, our sins are not removed until after our renewal through Sacramental Grace.
Then through our Act of Contrition, in which we promise to do our best to never sin again, the prayer of absolution, and enacting the penance, our sins are forgiven. John 20:23 says, 'If you forgive the sins of any, they are forgiven . . . '
Check out the Youcat, number 228 to find out more.