This is why confession is an important tool in freeing one of evil. Confession rids,cleans, and purifies the soul bringing us closer to God. In this verse, Jesus breathes upon the apostles and gives them the Holy Spirit. Confession gives the penitent a fresh start to perhaps work with a strong passion to never commit the sin. Not only does confession cleans the soul, it is pleasing to God and He fills the soul with graces.
Confession is the strongest tool of an exorcist.
In some instances, the individual is held in the state of possession because of a lack of unforgiveness on their part. Once the victim forgives all, he is freed or very close to being freed.