Tertullian

To a people which was very obdurate, and wanting in faith towards God, it might seem tedious, and even incredible, to expect from God that vengeance which was subsequently to be declared by the prophet: "Vengeance is mine; I will repay, saith the Lord." Therefore, in the meanwhile, the commission of wrong was to be checked by the fear of a retribution immediately to happen; and so the permission of this retribution was to be the prohibition of provocation, that a stop might thus be put to all hot-blooded injury, whilst by the permission of the second the first is prevented by fear, and by this deterring of the first the second fails to be committed.