If you missed part one, check it out here.

And when He had said this, He breathed on them, and said to them, “Receive the Holy Spirit. If you forgive the sins of any, they are forgiven them; if you retain the sins of any, they are retained.”John 20:22‭-‬23 NKJV

How does this verse above work?

This is the difference between forgiveness prior and after the crucifixion, the source.

The old covenant forgiveness was from us toward others.In the new we use the forgiveness of Christ and give it to others.

Just like we love others like we love ourselves in the old. But it the new we love others like God loves them.

This explains it well too :

that is, that God was in Christ reconciling the world to Himself, not imputing their trespasses to them, and has committed to us the word of reconciliation. Now then, we are ambassadors for Christ, as though God were pleading through us: we implore you on Christ’s behalf, be reconciled to God.II Corinthians 5:19‭-‬20 NKJV

So forgiveness is retained in us if we don’t give it to others, because they remain in condemnation. But if we forgive for the sake of Christ(not to gain or benefit ourselves) then Christ’s forgiveness becomes part of their life, just like Christ reconciled the world to Himself but gave us the word of reconciliation so those who would respond to the word we have can also have it for themselves.

If we receive Christ’s forgiveness over us, we will overflow to those around us. Because we don’t work for it, but we source forgiveness from Him.