Jesus gave only the Apostles the authorization to “forgive or retain sins” (John 20:23) and to bind or loose things in heaven and on earth (Matthew 18:18). But what do these words mean? Many misunderstand the nature of these commissions, forgetting that God alone can forgive sins (Isaiah 43:25).
Some believe these scriptures apply to themselves. Papacy believes that their priests on earth can acquit men of their sins. This is a serious error. This doctrine has led men to believe that any sin could be forgiven with impunity. The Apostles never exercised such control.
So, in what manner could the Apostles forgive sins? They, under the guidance of the Holy Spirit, would define the limitations of sin in their inspired writings. They tell us which sins are canceled by the merit of Christ's sacrifice and which sins are not cancellable. Whatever the Apostles forbade or allowed was under heavenly guidance and sanction.
Some sins lead to the second death. 1 John 5:16 (NLT), “If you see a Christian brother or sister sinning in a way that does not lead to death, you should pray, and God will give that person life. But there is a sin that leads to death, and I am not saying you should pray for those who commit it.”
Other sins require disciplines from God for teaching purposes. Luke 12:47-48 (NLT), "And a servant who knows what the master wants, but isn't prepared and doesn't carry out those instructions, will be severely punished. But someone who does not know, and then does something wrong, will be punished only lightly.”
The meaning of John 20:23 is not that the Apostles could forgive sins, but as inspired apostles, they would establish the church and declare the will of God respecting forgiveness of sins. They were not given the authority to forgive individuals. Jesus was promising to confirm all that the apostles taught, that all might have assurance of forgiveness who would comply with those terms. Those who did not comply should not be forgiven; their sins would be retained.