Catholics confess sins to priests because this is how God wants it to be. Looking through the bible you will see that this is how God wanted things to be in order for us to receive his forgiveness. For instance, in James 5:16, the word of God commands us to confess our sins to one another. Note it does not say to confess our sins directly to God nor does it say to confess your sins to God alone; it says confess your sins to one another.
In the story where Jesus cured the paralyzed man in Matthew chapter 9, Jesus demonstrates that he has all authority to forgive sins. The account of the healing of the paralyzed man ends by saying, "a feeling of great awe came over the crowd when they saw this, and they praised God for given such power to men." Note the Bible used the plural term "men" and not the singular "man".
I am a great fan of athletic games, my favourite being the 4 by 100 meters relay. I love to see the athletes powering down the track with the baton in hand, and passing it on to the next member of their team. I will remember for a long time, the men's finals in the last Olympics when Jamaica blew the competition away with a stunning run from start to finish. Anyway, every time I see such a race, I can't help but think to myself, "That's that Catholic Church!" No team can ever finish the relay race without the baton, nor can they just pick up any other object if their baton falls or gets lost. The same applies to the Catholic Church. Jesus ran the first leg and 'by golly' what a fantastic first leg he ran! The competition or should I say the opponents were completely left in the dust as he passed the baton on to the Church when he said in John 20: 21, "Peace be with you. As the Father has sent me, so am I sending you. After this, he breathed on them and said: "Receive the Holy Spirit. For those whose sins you forgive, they are forgiven; for those whose sins you retain, they are retained." You will recall in Matthew 9: 5-8, that God the Father sent Jesus with the authority to forgive sins. That is the baton in this relay race, where the ultimate prize is our salvation, and the baton - the authority to forgive sins - was handed to the early fathers of the Church by Jesus himself, and they passed it on to those who came after them. The baton is being passed on to this day, and will continue to the end of time.
Back to John 20:21, after Jesus breathed on them, after he had filled they with the Holy Spirit, he said to them, "For those whose sins you forgive, they are forgiven; for those whose sins you retain, they are retained." Why would Jesus make such a statement if they - the Church - did not have authority to forgive sins, and why would he give them authority to forgive sins if no one was expected to confess their sins to them? That would not make sense now would it?
So the bible does tell us to confess our sins to one another and that God gave men - our priests - the authority on earth to forgive sins. So when we as Catholics, we go to confesison and we confess sins to a priest, we are just simply obeying the plan set out for us by God himself through Jesus Christ his Son. God's power is at work in the priests who under the anointing of the Holy Spirit, forgives sins.
Ref: James 5: 16, Matthew 9: 1-8, John 20:21
