"Why should I give up revenge? On behalf of what? Moral princ..." — Andrzej Sapkowski quote meaning

Why should I give up revenge? On behalf of what? Moral principles? And what of the higher order of things, in which evil deeds are punished? For you, a philosopher and ethicist, an act of revenge is bad, disgraceful, unethical and illegal. But I ask: where is the punishment for evil? Who has it and grants access? The Gods, in which you do not believe? The great demiurge-creator, which you decided to replace the gods with? Or maybe the law? [...] I know what evil is afraid of. Not your ethics, Vysogota, not your preaching or moral treaties on the life of dignity. Evil is afraid of pain, mutilation, suffering and at the end of the day, death! The dog howls when it is badly wounded! Writhing on the ground and growls, watching the blood flow from its veins and arteries, seeing the bone that sticks out from a stump, watching its guts escape its open belly, feeling the cold as death is about to take them. Then and only then will evil begin to beg, 'Have mercy! I regret my sins! I'll be good, I swear! Just save me, do not let me waste away!'. Yes, hermit. That is the way to fight evil! When evil wants to harm you, inflict pain - anticipate them, it's best if evil does not expect it. But if you fail to prevent evil, if you have been hurt by evil, then avenge him! It is best when they have already forgotten, when they feel safe. Then pay them in double. In triple. An eye for an eye? No! Both eyes for an eye! A tooth for a tooth? No! All their teeth for a tooth! Repay evil! Make it wail in pain, howling until their eyes pop from their sockets. And then, you can look under your feet and boldly declare that what is there cannot endanger anyone, cannot hurt anyone. How can someone be a danger, when they have no eyes? How can someone hurt when they have no hands? They can only wait until they bleed to death.