I think it's necessary to repeat that one of the most important spiritual exercises possible is regular forgiveness.
By 'regular', I don't mean 'normal', but 'consistent'. What is really necessary is radical forgiveness.
Psychological studies have shown that forgiving someone of the wrongs they have committed against you improves your mental health. Christianity, Islam, Judaism, Buddhism, and a slew of other religions say that forgiveness is necessary for salvation or liberation. Clearly, it's a perennial phenomenon.
But allow me to introduce some metaphysics into this: the average person is a fundamentally neutral (but intellectual) psyche in the psychic plane, possessing (in descending order) an astral (emotional) body, an ethereal (life/orgone) body, and a physical body. Of course, we're 'trapped' in our physical bodies, but that's not the point.
The psyche can either become dark and eventually disintegrate into coarse matter, or it can become light and develop higher bodies: mental (higher emotional), causal (higher intellectual), and spirit (total unity).
Ruminating on wrongdoings serves the effect of blackening the psyche and dragging it back down toward matter. As Gurdjieff would say, it makes you 'food for the Moon'. Unforgiveness is spiritual poison. It disintegrates the self and leads to worse and worse karma.
So what does forgiveness do? Forgiveness is medicine for the soul. It purges karmic debt and loosens the grip of what some call the Matrix.
When someone does evil to you, they leave a karmic 'mark' on you alongside their own karma. It ties you to them. Unforgiveness strengthens this 'mark' until it becomes a monster; true forgiveness can quash the seed before it takes root and slay the dragon even after it has consumed you.
To be candid, I was raped as a child; I told whomever it was at the school that I felt more like a girl than a boy, and he proceeded to rape me multiple times. I have PTSD to this day from it. But, although I don't even remember his name, I forgive him. The mere act of forgiving my rapist has eased the horror quite a bit.
Forgiveness breaks chains of spiritual tyranny and relieves karmic debt. Perhaps, perhaps, if we could all forgive more often and more easily, we'd have a lot more awake people in this world.