Amen, only God can forgive sins, and Christ, being God alone has the immutable power to do so as well, but He never, as if he could of communicated any such authority to His disciples, nor did they ever assume any such authority to themselves.They completely knew that even though all Christians have the  treasure of that authority in them (Christ in us) it was never to be assumed it was of them ,just as in the same way God made Christ our wisdom, and although we do have His widsdom in us... it also is not of us. The same follows righteousness ,we have his rightousness, but will be found with no righteousness of our own

The key that the gates of hell could never prevail against that gives understanding to the meaning ofJohn 20 :23 lies in the previous two verses: It reads....“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.’”

Christ sent them, as He is sending us today to bring the good news of the way to salvation . Jesus was leaving the earth physically according to that temporal manifestation of flesh liked as sinful.But promised God would be with them in the person of the Holy Spirit living in them. Just as he was with the Father. As Christians proclaimed the gospel, they could honestly tell people who believed in that message that their sins were forgiven remited in accordance to God's word, the final authority , and they could honestly tell people that did not believe in the message that their sins were not forgiven but where retained and that they stand condemned in God’s eyes. Jesus said, “Whoever believes in the Son has eternal life, but whoever rejects the Son will not see life, for God’s wrath remains on him”