Why Forgive?

Choosing to retain anger and bitterness towards someone eats us up and makes us sick..... while the perpetrator of the offence goes free. Why do intelligent people take punishment upon themselves, rather than to let it go, and forgive? Forgiveness is not weakness or we would all do it. Forgiveness is not giving a pass to the other person. It's giving a pass to ourselves ..... to heal and go on.