Thanks for your question. Notice the context. Jesus had just been
raised the dead and returned to visit the apostles. He breathed on them giving them the
Holy Spirit. It was to them He said "If you forgive the sins of any, they are
forgiven them; if you retain the sins of any, they are retained." These men held
special place and power with the Lord. They would receive the baptism of the Holy Spirit
in Acts 2 as He had promised them. Because of their inspiration and miraculous power Jesus
gave them the right of forgiveness to others, because they were being guided by the Spirit
in what they said and did. It does not apply to other Christians.
I hope this helps.