When he celebrates the sacrament of Penance, the priest is fulfilling the ministry of the Good Shepherd who seeks the lost sheep, of the Good Samaritan who binds up wounds, of the Father who awaits the prodigal son and welcomes him on his return, and of the just and impartial judge whose judgment is both just and merciful. The priest is the sign and the instrument of God's merciful love for the sinner.
Source: Catechism of the Catholic Church (Vatican.va)