Human forgiveness and divine forgiveness are not the same. Human forgiveness accomplishes the improvement of the one doing the forgiving, regardless of its effect on the other. When I forgive my neighbor, a wound is healed in my spirit, even though my neighbor remain oblivious.
Divine forgiveness is different. God’s forgiveness accomplishes the improvement of the one being forgiven, even if the one being forgiven remains oblivious. God’s ways are not our ways, and our language so often obscures that reality.
Divine forgiveness is an ongoing blessing, a constant availability of God’s ministration, of the application to the individual of God’s loving concern for the condition of his or her spirit. Human forgiveness is the means of opening oneself to that ministration. The only means.
When we forgive, God’s love can bathe our spiritual wounds, whether self-inflicted or circumstantial. This does not make God’s love conditional on our behavior, it makes the agency of God’s love conditional on our attitude towards others. Jesus makes this point over and over.
The sin that’s unforgivable (in God’s reality), is being unforgiving (in our reality), that is, being unavailable to God’s ministration.