The Sins a priest cannot forgive
The Church has power to forgive sins and this authority is exercised by the members of her clergy to whom the Church has given the permission to do so.
Scripture: Jesus Christ Granted the Apostles His Authority to Forgive Sins
John 20:21 – before He grants them the authority to forgive sins, Jesus says to the apostles, “as the Father sent me, so I send you.” As Christ was sent by the Father to forgive sins, so Christ sends the apostles and their successors forgive sins.
John 20:22 – the Lord “breathes” on the apostles, and then gives them the power to forgive and retain sins. The only other moment in Scripture where God breathes on man is in Gen. 2:7, when the Lord “breathes” divine life into man. When this happens, a significant transformation takes place.
John 20:23 – Jesus says, “If you forgive the sins of any, they are forgiven. If you retain the sins of any, they are retained.” In order for the apostles to exercise this gift of forgiving sins, the penitents must orally confess their sins to them because the apostles are not mind readers. The text makes this very clear.
But there are some sins that the Church has reserved to the Pope and bishops to forgive. Some of them are as follows:
1. Physically attacking the Pope including attempting to assassinate him.
2. Breaking the “Seal of the Confessional” by a priest, i.e. violating the confidentiality of the confession by revealing the sins and identity of a penitent to anyone.
3. A priest absolving an accomplice in sin.
4. Participating in abortion which includes advising, paying for, or carrying out the act and after seeking admission into the order of priests or deacons in the Church. When someone who has committed this crime in the past wants to be ordained, they must first receive dispensation from the Pope.
5. Defiling the Eucharist, the Body and Blood of Christ is extremely grievous and can be dealt with only by the Pope.