It requires honesty to see whether you still harbor grievances, whether there is someone in your life you have not completely forgiven, an “enemy.” If you do, become aware of the grievance both on the level of thought as well as emotion, that is to say, be aware of the thoughts that keep it alive, and feel the emotion that is the body’s response to those thoughts. Don’t try to let go of the grievance. Trying to let go, to forgive, does not work. Forgiveness happens naturally when you see that it has no purpose other than to strengthen a false sense of self, to keep the ego in place. The seeing is freeing. Jesus’ teaching to “Forgive your enemies” is essentially about the undoing of one of the main egoic structures in the human mind.
The past has no power to stop you from being present now. Only your grievance about the past can do that. And what is a grievance? The baggage of old thought and emotion.

~Eckhart Tolle (A New Earth )