Musar su Deuteronomio 13:9

“Show him no pity or compassion, and do not shield him” (Deuteronomy 13:9). We were warned with this to not have compassion nor to have mercy on those that cause people to sin and stumble. And our Rabbis, may their memory be blessed, said (Midrash Tanchuma, Metzora 1), “Anyone who becomes merciful upon the cruel will end up being cruel to the merciful.”

Another among the qualities of the soul is cruelty. One must be cruel and hard to those who entice him and make him go astray. And he should have no mercy upon the wicked, as it is said (Deuteronomy 13:9), “Neither shalt thou spare, neither shalt thou conceal him.”

But there is a kind of mercy that is worse than cruelty. For example, when one has mercy on the wicked and strengthens them. And there is a great stumbling block before the one who raises up the wicked and gives them his hand and abases and rejects the good, and on this it is said in the Torah: "Neither shall thine eye pity him, neither shalt thou spare, neither shalt thou conceal him" (Deut. 13:9). Nor shall one have mercy upon the poor in the course of a law suit, but judge the case fairly, as it is written: "Neither shall you favor a poor man in his cause" (Exodus 23:3), which means that he should not prevert justice because of sympathy with the poor man's distress. And there is mercy which is cruelty. For example, when one gives alms to a poor man and afterwards burdens the poor man by saying, "I gave you this and this; now you must do something for me and serve me just like all that I did for you." And of this type of mercy it is said : "The mercies of the wicked are cruel" (Prov. 12:10).