General Catholic
Why confess sins to a priest instead of directly to God?
Catholics do confess directly to God, but Christ gave the apostles the authority to forgive sins in his name, and priests exercise that same delegated authority received from the apostles.
Catholic teaching
In the Sacrament of Reconciliation, the priest acts as Christ's minister, pronouncing God's own forgiveness through the ministry Christ instituted; it also provides the penitent with pastoral guidance, humility, and assurance of God's mercy.
Biblical foundation
The risen Christ breathed on the apostles saying, 'Receive the Holy Spirit. If you forgive the sins of any, they are forgiven' (John 20:22-23), a real transfer of authority that would be meaningless if confession were only ever private between the sinner and God.
Scripture references
Historical evidence
The Didache (c. AD 100) already instructs Christians to 'confess your sins in church,' and Tertullian and Cyprian in the third century describe formal confession to bishops as an established practice.
The Church Fathers
“Let each confess his sin while he is still in this world, while his confession can be received.”