John 20:21-23  Again Jesus said, "Peace be with you! As the Father has sent me, I am sending you." And with that he breathed on them and said, "Receive the Holy Spirit. If you forgive anyone his sins, they are forgiven; if you do not forgive them, they are not forgiven."

Some Catholics use these verses to try to justify the practice of confession. They say that Jesus gave the apostles the authority and power to forgive sins on his behalf. They then merge that into a doctrine of apostolic succession, which says that the same authority and power has been passed on from the original apostles to today’s bishops and priests. So they believe that the priest has the authority and power to forgive the sins that are confessed to him. 

However, that is not what this verse is about. Jesus cannot be saying that the apostles can forgive sins, because only God can do that (Luke 5:17-26).  Instead, Jesus was commissioning the apostles to declare that those who repent and believe in Jesus Christ can be assured of forgiveness, and those who refuse to repent and reject Jesus can be assured that their sins are not forgiven.  In that way, the apostles and all who carry on Christ’s ministry to the world, have the authority to proclaim the message of the Gospel by the power of His Holy Spirit. This same authority is given to all believers, not just to a select few, as each Christian can confidently declare this exact same message, that sin is forgiven by Jesus when we repent and trust in Him.