Midrash sa Exodo 17:13: Bamidbar Rabbah, Mekhilta DeRabbi Yishmael, Midrash Tanchuma & Midrash Tanchuma Buber

Another matter: “However, the tribe of Levi you shall not count” (Numbers 1:49) – why were they not counted with Israel? It is because the tribe of Levi was the palace guard. This is analogous to a king who had several legions, and he said to his chief of staff: Go count the legions, except for the legion that stands before me. That is why the Holy One blessed be He said to Moses: “However, the tribe of Levi [you shall not count]…among the children of Israel” (Numbers 1:49). Among the children of Israel you shall not count them, but by themselves, count them, as it is not in keeping with the king’s honor that his legion should be counted with the legions. That is why Israel was counted by itself and the tribe of Levi was counted by itself.
From where do you say that it is for that reason that He said it to him? It is because it is written thereafter: “And you, appoint the Levites over the Tabernacle of the Testimony…” (Numbers 1:50). When the Holy One blessed be He said to Moses: “However, the tribe of Levi you shall not count…” (Numbers 1:49), Moses grew afraid and said: Is there perhaps a disqualification in my tribe, due to which the Holy One blessed be He does not wish me to count them? The Holy One blessed be He said to Moses: I said so to you only to exclude them from the decree, so that they will not die with them. That is what is written: “And you shall not take a census of them [ve’et rosham lo tisa] among the children of Israel” (Numbers 1:49). Why? It is because the Levites are Mine: “The Levites shall be Mine” (Numbers 3:12, 45). As, anyone who draws Me near, I draw him near. They drew near to Me, as it is stated: “Moses…said: Whoever is for the Lord, come to me; and all the sons of Levi gathered to him” (Exodus 32:26). They drew Me near, and I draw them near: “The Levites shall be Mine.” Moreover, because they were found to be loyal to Me, as they observed my admonition: “You shall have no other gods…” (Exodus 20:3), therefore, they are worthy to be the trustees of My house. “And you, appoint the Levites [over the Tabernacle of the Testimony…and they shall encamp around the Tabernacle]” – likewise it says: “My eyes are on the faithful of the land; they will dwell with Me.” (Psalms 101:6).
You find that anyone who is put to the test regarding a matter,¹⁷And he passes the test. the Holy One blessed be He loves him forever. As, you find regarding Joshua that he was put to the test with Amalek, and he performed there in accordance with the Torah and the mitzva, as it is stated: “Joshua weakened [Amalek and its people by sword]” (Exodus 17:13). The Omnipresent said to him: From your tribe, I will establish one who will exact retribution against Amalek forever: “From Ephraim came those who uprooted Amalek” (Judges 5:14). Saul, who was put to the test but did not properly fulfill his command, but rather: “Saul and the people spared [Agag…and all that was good, and would not utterly destroy them]” (I Samuel 15:9), He caused him to fall back [le’aḥorav], and his kingdom was taken from him: “After you [aḥarekha], Benjamin” (Judges 5:14).
This tribe, too, I put them to the test, and they were found observant, and they gave their lives for sanctification of My name, as it is stated: “Each man, place his sword upon his thigh…[and each slay his brother, each his neighbor, each his relative]. The sons of Levi acted in accordance with the word of Moses…” (Exodus 32:27–28); “Who said of his father, and of his mother: [I did not see him, and his brothers he did not recognize, and his children he did not know, because they observed Your saying, and Your covenant they upheld]” (Deuteronomy 33:9). Here, too, I will draw them near and make them My palace guard, and I entrust My sanctity and the function of My house to them. That is what is written: “And you, appoint the Levites [over the Tabernacle of the Testimony]” (Numbers 1:50). Why? It is because they are loyal to Me. During its dismantling and its erecting, too, I do not want others to dismantle it and erect it, only them. That is what is written: “And when the Tabernacle travels, [the Levites shall dismantle it, and when the Tabernacle encamps, the Levites shall erect it]” (Numbers 1:51). Is it possible that the mitzva is incumbent upon the Levites, but if an Israelite did so it is permitted? The verse stated: “And the stranger who approaches shall be put to death” (Numbers 1:51). Likewise it says: I hate doers of perversity” (Psalms 101:3) – this is Israel that strayed from after the Omnipresent and crafted the calf, and the Holy One blessed be He despised them from being His trustees.
Do not say that it was that Israel would not touch it [only] during the journeys, rather, also during the encampments, only the children of Levi would approach it. That is what is written: “The children of Israel shall encamp, each in his camp.… And the Levites shall encamp around the Tabernacle of the Testimony” (Numbers 1:52–53). Why do I caution them that Israel should distance themselves from the Tabernacle? It is so there would not be fury upon them, as they are unworthy to approach it. That is what is written: “And there will not be fury against the congregation of the children of Israel” (Numbers 1:53). But the Levites will protect it; that is what is written: “The Levites will protect the watch of the Tabernacle of the Testimony” (Numbers 1:53). “The children of Israel did according to everything that the Lord commanded Moses, so they did” (Numbers 1:54) – as they distanced themselves from the Tabernacle and provided room for the Levites to encamp around the Tabernacle.

(Exodus 17:13) "And Joshua weakened ("vayachalosh") Amalek and his people ('amo')": R. Yehoshua says: He descended and decapitated his heroes, who stood with him in the ranks of war.

(Numb. 31:2:) “Exact vengeance [for the Children of Israel on the Midianites; afterward you shall be gathered unto your people].” R. Judah said, “If Moses had wanted to live for several [more] years, he could have remained alive; as the Holy One, blessed be He, had made his death dependent upon the vengeance against Midian.⁷Numb. R. 22:2. It is simply to show you the praise of Moses, as he did not say, ‘For the sake of my remaining alive, I shall delay the Children of Israel's vengeance on Midian.’ [Rather] immediately (in vs. 3), ‘Moses spoke unto the people, saying, “Arm some of your number (anashim) for the army, and let them fall on Midian.”’” [The word,] anashim, [implies that they were] righteous. So also elsewhere (in Exod. 17:9), “Choose anashim for us,”⁸Here also, as in Numb. 31:3, anashim implies that those chosen were righteous. [implies] righteous men. And so too (in Job 4:13), “in the falling of slumber upon anashim.” (Numb. 31:3, cont.:) “To render the vengeance of the Lord against Midian.” The Holy One, blessed be He, had said (in vs. 2), “the vengeance of the Children of Israel”; but Moses says (here in vs. 3), “the vengeance of the Lord.” The Holy One, blessed be He, said to them, “It is your judgment that is called for, because they caused Me to harm you.” [But] Moses said, “Master of the world, if we had been uncircumcised or practitioners of star worship or had denied [the binding force of] the commandments, they would not have persecuted us. On the contrary, [they have done so precisely] because of the Torah and commandments which You have given. The vengeance, therefore, is Yours.” Ergo (in Numb. 31:3), “to render the vengeance of the Lord against Midian.” (Numb. 31:4:) “[You shall send to the war] a thousand per tribe [from all the tribes of Israel].” Some say, “He sent two thousand from each and every tribe.” But others say, “Three thousand from each and every tribe, with twelve thousand armed shock troops, twelve thousand to guard the baggage, and about them it is stated (in Cant. 4:2), ‘Your teeth are like a flock of ewes…,’ and twelve thousand for prayer.”⁹Numb. R. 22:3. And where is it shown? Where it is stated (ibid.), “A thousand per tribe (literally, a thousand per tribe; a thousand per tribe).”¹⁰For the third thousand per tribe, Numb. R. 22:3 cites Numb. 31:5, which repeats: A THOUSAND PER TRIBE, for the third time. (Numb. 31:5:) “So from the thousands in Israel there were furnished a thousand per tribe.” What is the meaning of “were furnished?” That they were furnished for each other in pairs.¹¹Gk.: zeuge, zuga; Lat.: jugera. The probable meaning is that for each thousand who fought, there were a thousand replacements. Another interpretation [of “were furnished”]: They were furnished by force. Since Scripture had made the death of Moses dependent upon the vengeance against Midian, they said, “Shall we go against Midian and let Moses die?” They refrained from going. The Holy One, blessed be He, said to Moses, “Cast lots over the tribes, and they will be furnished automatically.” (Numb. 31:6:) “Then Moses sent them, a thousand per tribe [along with Phinehas ben Eleazar].” The Holy One, blessed be He, said to Moses (in vs. 2), “’Take vengeance,’ by yourself,” and he sent others?¹²Numb. R. 22:4. It was simply because he had been raised in Midian, he said, “It is not right for me to oppress those who have done good to me.” The proverb says, “Do not cast a stone into a cistern from which you have drunk water.” But some say that this is not the same Midian in which Moses was raised. As this one is next to Moab and it is [still] desolate until now. And why did He send Phinehas (instead of someone else)? He said, “Whoever has begun a commandment should finish it. [Phinehas] has (according to Numb. 25:11) ‘turned around My wrath’ (by executing an Israelite man copulating with the Midianite woman). Let him finish the commandment [that he undertook].” (Numb. 31:6, cont.:) “And the vessels of the sanctuary (haqodesh).” This refers to the ark (and its contents), since it is stated (in Numb. 7:9), “because they (i.e., the Children of Kohath) had the service of the holy (haqodesh) objects, which they carried on the shoulder.” R. Johanan said, “These were the priestly garments, in which were the urim and thummim, as stated (in Exod. 29:29), ‘And the sacred (haqodesh) garments of Aaron.’” (Numb. 31:8:) “They also killed Balaam ben Beor with the sword.” Now what was he doing there? He had simply gone to receive a reward for the twenty-four thousand from Israel that had fallen through his counsel. And about him is it stated (in Prov. 26:27), “He who digs a pit will fall in it.” [It is like the] proverb about the camel that goes to put on and claim horns, while the ears that it had are severed from it. (Numb. 31:11-12:) “Then they took all the plunder…. And they brought unto Moses and Elazar the Priest.” [This text serves] to show their excellence, for they did not want to take the spoils without permission. Rather they had brought all of it before them; and [only] after that, they took [them with his permission]. (Numb. 31:13:) “Then Moses, Elazar the Priest, and the princes of the congregation [went out to meet them.” This text serves] to show Moses' humility, for they all were disciples of his disciples.