Forgiveness is part of the action of the Holy Spirit in our lives. More accurately, it is the action of Christ through the Holy Spirit in our midst. By the power of the Spirit, Christ is present both forgiving us and forgiving through us. The Spirit is given to us by Christ himself. He breathed upon the disciples and they received the Holy Spirit.
In one of her books, Corrie Ten Boom tells of meeting the guard from the concentration camp where she and her family had been held by the Nazis. She had been speaking at a large church meeting, and after the meeting he had come forward. He put out his hand to her, and she instinctively pulled back, remembering the horrors to which that hand had been put or in which it had cooperated, but then, she testified, something came over her, she knew not what, and she reached out and grasped his hand and extended her forgiveness as the tears rolled down his cheeks.
There will be those who say this is merely sentimental and who grit their teeth, as they demand more obvious vengeance; I cannot judge them. I only know that to forgive in such a manner is beyond human comprehension; it is the work of God and can only be done by us through the grace of God at work in us. Nor, is it an attitude we Christians carry around with us all the time, like little Mary Sunshines. Corrie Ten Boom received the grace to forgive in the moment the grace was needed, and not before. Our Lord, upon the cross, forgave his executioners while he was being nailed to it; there was no plenary absolution in advance. Forgiveness, like the resurrection, breaks in upon us through shut doors.
We are called and sent to participate in Christ's message of forgiveness because we have been forgiven. "As the Father has sent me, even so I send you." Christ was sent to be the agent of reconciliation, and we are to be such agents in the world. It seems to me a sad fact that forgiveness has been for sale in the church during so much of its history, when it should have been given away.