Confession
John 20:21-23
As the Father hath sent me, I also send you... Receive ye the Holy Ghost. Whose sins you shall forgive, they are forgiven them; and whose sins you shall retain, they are retained.
Context of the passage
On the evening of the Resurrection, Jesus appears to the apostles and confers on them the power of the Holy Spirit for the forgiveness of sins.
Catholic reading
Jesus gives the apostles the actual authority to forgive or retain sins, which requires knowledge of the specific sin, implying a spoken confession, the direct scriptural institution of the Sacrament of Confession administered by ordained priests.
Common objection
This authority was only for the apostles personally to preach the Gospel, by which sins are forgiven or retained depending on belief, not a sacramental power passed to priests.
Response
The distinct twofold power to either 'forgive' or specifically 'retain' cannot be reduced to general Gospel preaching, since preaching offers forgiveness to all who believe; retaining implies a discerning judgment case-by-case, requiring a hearing of specific sins as in sacramental confession.