The Catechism of the Catholic Church teaches the following.

1455 The confession (or disclosure) of sins, even from a simply human point of view, frees us and facilitates our reconciliation with others. Through such an admission man looks squarely at the sins he is guilty of, takes responsibility for them, and thereby opens himself again to God and to the communion of the Church in order to make a new future possible.

1456 Confession to a priest is an essential part of the sacrament of Penance: "All mortal sins of which penitents after a diligent self-examination are conscious must be recounted by them in confession, even if they are most secret and have been committed against the last two precepts of the Decalogue; for these sins sometimes wound the soul more grievously and are more dangerous than those which are committed openly."

Some people have a difficulty in seeing the necessity of confessing  one's sins to a priest, rather than to God directly. This is similar to those disciples who found it heard to believe when Jesus told them that he would give his Body to eat and his Blood to drink. It is Jesus who gave his Apostles the power to bind and to loose on earth. Why would Jesus do this?

First, as human beings we don't like to live in uncertainty. We want assurance. If we have certain symptoms, we fear we may have contracted the Delta virus. To know for certain we go to a Doctor to be tested. We are relived when he assures us that the test was negative. To confess our sins to a priest gives us the assurance in faith that God in his mercy has forgiven us our sins. We receive the sign of the cross absolving us from our sins. Without this, we hope we are forgiven by confessing them to God directly, but there is no sign. Recall the scene when the paralytic was brought to Jesus. He forgave his sins. Some observers objected. Then he gave a sign assuring the man that his sins were forgiven. He healed him. Did we not feel relived and at a peace, when we heard the words of absolution? In faith, did we not feel something lifted from our heart? Jesus knows we need assurance and so, through the ministry of the priest, he gives us this sign of forgiveness. Thank you Jesus!