Revenge is the expression and continuation of resentment. Resentment is the deliberate or settled anger over a hurt or injury inflected. It may lead to tit for tat repayment for injury or restitution as a debt due to the injured person. Frequently it goes beyond this. It is not the anger that injures but the continued nurtured resentment which leads to lust for revenge. The growth of criminal law is in part an attempt to remove from private hands revenge and replace it with public retribution and appeal to public law, protecting the weak from the strong. Once public law has been established revenge itself becomes a crime. From the moral perspective revenge is seen as wrong because it is anti-social leading to human misery and not human happiness. It is almost always unjust because the judge is the injured person and takes an exaggerated estimate of his injuries. It is self-destructive because it is essentially selfish. It prevents any development of a charitable and forgiving temper. From a religious perspective it is frequently seen as interfering with the prerogative of God.
From one perspective revenge is a primitive form of law. It is unbridled, unreflective and an arbitrary act of retribution. Punishment, within the framework of law, has a purpose, is administered according to established guidelines and is dispensed on the basis of a judicial sentence. Moving from vengeance to penal law is a moral advance.
Others argue that revenge is for those outside the legal system of a group or community. The laws of the group punish transgressors within the community. Revenge is an act of self-assertion by a group against an outside attack. As such it can be an act of exclusion. The person harmed and his avenger, on one hand, and the culprit, on the other, are members of different groups. Each represents the rights and duties of the group and acts in its name.