God forgives us freely and completely because of Christ death on the cross. Sometimes others are not so free and complete in their forgiveness of us. It hangs over our head every time me encounter that person. We must make sure we accept the forgiveness of Christ for us and aren't judging ourselves.
God says that He who is forgiven much loves much. The person who sees how much Jesus has forgiven them is more free to forgive others. They have a greater compassion because of Christ compassion on them.
Forgiveness is a process sometimes. But one we should enter into because it not only sets the other person free it sets us free. Those who have sinned and those who have been sinned against.