Midrasch zu Nachum 1:2

“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].”

R’ Elazar said: the whole Torah hangs on judgment. That is why the Holy One gave the laws of justice after the Ten Commandments - because people cross the line of justice, are punished and this teaches the whole world. Sodom was not overturned until it crossed the line of justice, as it says “…pride, abundance of bread, and careless ease…“ (Ezekiel 16:49) Even Jerusalem was not exiled until she crossed the line of justice, as it says “…the orphan they do not judge, and the quarrel of the widow does not come to them.” (Isaiah 1:23) And why did the Holy One give the crown to Yehudah? He is not the sole mighty one from among his brothers, are not Shimon, Levi and the others mighty as well? Rather, it was because he gave true judgment to Tamar, therefore he was made judge of the world. This is like a judge before whom an orphan’s judgment comes and he finds in her favor. So too Yehudah – Tamar’s judgment that she should be burned came before him, and he found in her merit because he found merit in her. How? Yitzchak and Yaakov were sitting there, and all his brothers were covering for him. Yehudah acknowledged Gd (HaMakom) and spoke the truth of the matter, saying “She is more in the right than I…” (Bereshit 38:26) and the Holy One made him prince. So Ben Zoma used to say and explain: if you were ashamed in this world, you will not be ashamed of the Holy One, who is a consuming fire, in the coming world. Why? Because the shame of this world is nothing other than the shame of one’s standing in the coming world, as it says “For this let every pious man pray to You…” (Tehillim 32:6)

Another opinion: “The Lord tests the righteous.” – This is Abraham – “Sometime after these things, God tested Abraham.” R. Avin expounded: (Ecclesiastes 8:4) “Since a king's word is supreme, who can say to him: ‘What are you doing?’” – R. Avin said: [This may be compared] to a teacher who commands his student, saying to him: (Deuteronomy 16:19) “You shall not judge unfairly,” but [the teacher himself] judges unfairly; (Deuteronomy 16:19) “Do not take a bribe,” but [the teacher himself] takes a bribe; Do not lend on interest, but [the teacher himself] lends on interest. His student said to him: Rabbi, you said to me: Do not lend on interest, but you lend on interest? [Is it] permitted to you but forbidden to me? [The teacher] said to him: I said to you: Do not lend on interest to a Jew, but you may lend on interest to an idol worshipper, as it is written: (Deuteronomy 23:21) “You may lend on interest to a foreigner, but you may not lend on interest to your brother [Israelite].” Thus Israel said before The Holy One Blessed be He: Master of the Universe, you wrote in your Torah: (Leviticus 19:18) “You shall not take vengeance or bear a grudge,” but you take vengeance and bear a grudge, as it is said: (Nahum 1:2) “The Lord is vengeful and fierce in wrath. The Lord takes vengeance on His enemies.” The Holy One Blessed be He said to them: I wrote in the Torah: (Leviticus 19:18) “You shall not take vengeance or bear a grudge against your countrymen,” but I take vengeance against idol worshippers – (Numbers 31:2) “Avenge the Israelite people on the Midianites.” It is written: (Deuteronomy 6:16) “Do not test the Lord” – [but] “God tested Abraham.”

(Bamidbar 31:2) "Afterwards you will be gathered unto your people": We are hereby apprised that Moses' death was contingent upon the defeat of Midian — in spite of which he entered into it with zeal, viz. (Ibid. 3) "And Moses spoke to the people, saying 'hechaltzu,'" connoting zeal, as in (Devarim 3:18) "Chalutzim shall you cross over." (Ibid.) "And let them be against Midian to execute the vengeance of the L-rd against Midian": He told them: You are not executing the vengeance of flesh and blood, but the vengeance of Him who spoke and brought the world into being, as it is written (Nachum 1:2) "the L-rd is a G-d of scorn and revenge."