I would like to cordially thank my dear friend Susan Whigham for the discussion.
Forgiveness is the letting go of feelings of getting hurt. It's allowing yourself and others to heal instead of ruminating and dwelling on the damage which has been done.
Vengeance is trying to return the damage to the persons or factors which are supposedly responsible for it with all your might and energy.
It's well known that forgiveness brings real closure. Vengeance never does, because an eye for an eye leaves the whole world blind in a matter of few days.
Forgiveness is wisdom and vengeance is ignorance.
It's important to understand that both of them are illusions. They're two sides of same coin. They are because you don't understand yourself fully. Take for example, Law of Karma. If you think you forgive others or universe and the universe forgives you--this is a righteous understanding of it. Even better is to understand that whatever happens to you is because of your thoughts. The universe out there(provided you consider that there is a universe independent of you!) is neutral to everyone. If you harness from it you would realize that there is really nobody to thank or blame for good or bad that seems to happen with you.
There is just one reality. You are dreaming that there are others. The truth is that you alone are. Vengeance is trying to struggle with yourself whereas forgiveness is allowing yourself to be. If you just realize that whatever you give you give to yourself it becomes so easy to understand.
You might have read that Karma is a bitch. It acts like a boomerang. What goes around comes around! It's because there is nothing else--you alone are projecting a universe. Inside your mind everything exists. Whatever you give to yourself you receive back because there is nobody else to take. If you give love, kindness, warmth and smile that is what you get back and if you give suspicion, hatred, violence and anger that is what you get back. It's so because whatever you give you give to yourself.
Since you're dreaming you see two directions of movement--one leads you towards the freedom or liberation--it's a movement in wisdom. The other is what makes your dream nightmarish --an eye for an eye--it's a movement in ignorance. They both exist inside the dream but one of them, the movement in wisdom is a sign of awakening.
If someone very clearly understands the Karma, it becomes clear that he alone is responsible for his all feelings and it becomes clear that there is actually no need of forgiveness because there is no offender in the first place. It's so because Karma is deeply associated with awakening--Karma is advocate of one reality--it's based on the realization that you alone are and whatever you think you're doing you're with yourself.
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