Midrash su Levitico 19:18

R. Jochanan, in the name of R. Simon b. Jochai, said: "A scholar who taketh no revenge or bears no grudge (Fol. 23) like a serpent, cannot be called Talmid Hacham (a scholar)." Behold, it is written (Lev. 19, 18) Thou shalt not avenge nor bear any grudge. This is written in regard to monetary matters, as we are taught in the following Baraitha: What is called revenge, and what is called bearing a grudge? Revenge: When one comes to the other, saying, "Lend me thy spade," and he says, "Nay." On the morrow, the second comes to the first, and asks of him to borrow his axe. He answers, "I do not wish to lend to you, as you have not lent to me." This is called revenge. What is bearing a grudge? When one comes to another, saying, "Lend me thy sickle," and he says, "Nay." On the morrow the second comes to the first, and wants to borrow his spade. He answers, "I lend it to you, because I am not like you, who did not want to lend me yesterday." This is called bearing a grudge. And in cases of bodily pain, has not the Torah forbidden vengeance? Have we not been taught in the following Baraitha: Those who are insulted, and do not insult others; hear themselves reviled, and do not reply; perform their duties out of love, and accept with joy, afflictions, concerning them Scripture says (Jud. 5, 31) Those that love him are as the rising sun in his might. By the above is meant that one may bear a grudge in his heart. But has not Raba said: "He who passes over his retaliations (who forbears to retaliate), all his transgressions will be pardoned." The latter refers to a case when the offender asks to be pardoned and he complies with the offender's request.

“Since the king's word has power, and who will say to him: What are you doing” (Ecclesiastes 8:4).
“Since the king's word has power.” Rabbi Bon said: It is written: “Do not test [the Lord]” (Deuteronomy 6:16), “and God tested [Abraham]” (Genesis 22:1), “Do not take vengeance and do not bear a grudge” (Leviticus 19:18), “the Lord is a zealous and vengeful God” (Nahum 1:2). [This is analogous] to a rabbi who would command his disciple, and say to him: ‘Do not divert judgment,’ but he [the rabbi] diverts judgment; ‘do not give preferential treatment,’ but he gives preferential treatment.²²A parallel midrash (Bereshit Rabba 55:3) adds the example: The rabbi tells him not to lend with interest, but he lends with interest. The disciple said to him: ‘Rabbi, for you it is permitted and for me it is prohibited?’ [The rabbi] said to him: ‘I am telling you only that you may not lend to an Israelite with interest, but lend to a gentile, as it is written: “You may take interest from a gentile” (Deuteronomy 23:21).’²³Thus, the rabbi informs his disciple that he did not fully understand any of the rabbi’s actions. So too, Israel said before the Holy One blessed be He: ‘Master of the universe, did You not write in Your Torah: “Do not take vengeance and do not bear a grudge” (Leviticus 19:18)? But You take vengeance and bear a grudge.’ He said to them: ‘I will not bear a grudge against Israel, as it is written: “He will not contend to eternity or forever bear a grudge” (Psalms 103:9); however, for the nations of the world: “The Lord is vengeful to His foes and bears a grudge against His enemies” (Nahum 1:2). I dictated to you in My Torah: “Do not take vengeance and do not bear a grudge against the members of your people” (Leviticus 19:18), but you may take vengeance against the nations of the world, as it is stated: “Avenge the children of Israel [on the Midianites]” (Numbers 31:2),’ to realize what is written: “Since the king's word has power, [and who will say to him: What are you doing].”

4) "shall be to you the stranger that lives among you. And you shall love him as yourself." Just as it is written of Jews (Vayikra 19:18) "and you shall love your fellow as yourself," so is it written of proselytes "and you shall love him as yourself." "for you were strangers in the land of Egypt": Know the soul of the strangers, for you yourselves were strangers in the land of Egypt."