Criteria For Revenge

When outrage and fury impel you to take revenge, your emotion is rooted in a sense of pride. You are enraged because you have been offended, and your pride has been hurt. A person who is truly humble regards himself as nothingness and takes vengeance only if G-d's honor is maligned. Consequently, before you zealously take up G-d's cause you must meet two important criteria: you must be free of any trace of anger and must not possess any haughtiness.

(Yismach Moshe)