Forgiveness is a word that is often misunderstood within the context of A Course in Miracles.
Forgiveness does not mean forgiving others for what they did to us. It's not about taking the high road and being a better person.
Rather, forgiveness in the course is the recognition that nothing happened. Forgiveness is the awareness that our true nature - our true identity - is mind, not this body. And more specifically, a decision-making mind that in every moment is choosing either the ego or the mind of spirit.
So, forgiveness is the process of returning to the decision-maker in our mind and choosing against the ego and for the holy spirit.
The ego is what tells us that something did happen. People did sin against us. And we either need to damn them or forgive them. And this form of forgiveness, of course, is not forgiveness at all. It's really a judgment masquerading as forgiveness. "You hurt me. But in my wonderful beneficence I'm going to overlook it. But don't you ever forget it. Because I certainly won't."
When we choose against the ego, we no longer see ourselves - or anyone else - as a body. We see the love that unites everything. And from this perspective, there can't possibly be anything that needs to be forgiven. Because now we've returned to the light. We see that we are the light of the world, and everything is a part of that light.
And as we learn in this lesson, when we recognize our function - which is to return to our mind and choose the holy spirit - then we will experience true happiness.