מדרש אויף במדבר 4:1

וַיְדַבֵּ֣ר יְהוָ֔ה אֶל־מֹשֶׁ֥ה וְאֶֽל־אַהֲרֹ֖ן לֵאמֹֽר׃

און גאָט האָט גערעדט צו משהן און צו אַהרֹנען, אַזױ צו זאָגן:

Sifra

1) "And He called to Moses and the L–rd spoke to him, etc." "to him" — to exclude Aaron. R. Yehudah b. Betheira said: Thirteen dibroth (accompanied by a command) were stated in the Torah to Moses and Aaron, and, corresponding to them, thirteen limitations, to teach us that they were not spoken to Aaron, but to Moses, to tell them to Aaron. (The dibroth: 1) [Shemoth 6:13]; 2) [Shemoth 7:8]; 3) [Shemoth 9:8]; 4) [Shemoth 12:1]; 5) [Shemoth 12:43]; 6) [Vayikra 11:1]; 7) [Vayikra 13:1]; 8) [Vayikra 14:33]; 9 [Vayikra 15:1]; 10 [Bamidbar 2:1]; 11 [Bamidbar 4:1]; 12 [Bamidbar 4:18]; 13) [Bamidbar 19:2].)
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Bamidbar Rabbah

“The Lord spoke to Moses and to Aaron, saying” (Numbers 4:1).
“The Lord spoke to Moses and to Aaron, saying” (Numbers 4:1) – because all the action in this portion involved Aaron, He included Aaron in the Divine Speech, as that is the principle: Anytime the Divine Speech is to the priests, the action involves the priests.
“Take the census of the sons of Kehat from among the sons of Levi, by their families, by their patrilineal house” (Numbers 4:2).
“Take the census of” – it does not say count [pekod], but rather, “Take the census of [naso et rosh],” an expression of elevation [nesiut]. When they were counted to be appointed over the Tabernacle service, they received an elevation.
“From among the sons of Levi” – as from all of the sons of Levi, none were as important as the sons of Kehat. From them were priests and Levites. Because they were important, and moreover, their service was with items of the most sacred order, that is why they were counted first. As you find that when He counted them from one month old in order to redeem the firstborn, they were counted in accordance with their birth order: Gershon first, then Kehat, and then Merari. But here, when He counted them to appoint them over the sacred vessels, He counted them in accordance with the significance of their service. Kehat, because it was appointed over the Ark and items of the most sacred order, was privileged to be counted first. After him was Gershon, who was the firstborn and was appointed over the sheets and the Tent of Meeting, and after him was Merari, who was appointed over the beams, the bars, the pillars, the bases, and the pegs.
“From thirty years old and above and until fifty years old, all those enlisted for duty, to perform labor in the Tent of Meeting” (Numbers 4:3).
“From thirty years old and above…” and one verse says: “From twenty-five years old and above” (Numbers 8:24). How can these two verses coexist? It is from twenty-five years for study, from thirty for service.
“This is the service of the sons of Kehat in the Tent of Meeting: Items of the most sacred order” (Numbers 4:4).
“This is the service of the sons of Kehat…” – because Kehat merited that Aaron, who was of the most sacred order, emerged from him, that is why his descendants merited that their service was with items of the most sacred order.
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Bamidbar Rabbah

“Moses, Aaron, and the princes of the congregation counted the sons of the Kehatites by their families, and by their patrilineal house” (Numbers 4:34).
“Moses, Aaron…counted.” Immediately Moses and Aaron acted, and they counted the sons of the Kehatites first, just as the Holy One blessed be He said to them. From where is it derived that the Holy One blessed be He said to both of them to count them? It is as it is stated: “The Lord spoke to Moses and Aaron saying: Take a census of the sons of Kehat” (Numbers 4:1–2).
Why is speech stated regarding Kehat and Gershon, but is not stated regarding Merari?16The verses contain direct speech by God to Moses and Aaron referring to two of the sons (Numbers 4:1-2, 21-22), but only an indirect reference for the third (Numbers 4:29). It is in order to accord honor to Gershon and to liken him to Kehat. Why is Aaron not stated in the speech regarding the sons of Gershon as it is stated regarding the sons of Kehat? It is because Aaron is excluded from all the speeches that were stated to Moses, as the Divine Presence did not speak with Aaron. Why, then, are there several places where Aaron is written? It is not that the speech was with Aaron, but rather, in every portion that relates to Aaron, “Aaron saying” is written. The Holy One blessed be He said to Moses, so that he would say to Aaron. This is why Aaron is written in the speech to the sons of Kehat. It is because every burden of the sons of Kehat and all their service was given to them by Aaron and his sons, as they were not permitted to touch the Ark and all the vessels until Aaron and his sons would cover them, just as it says: “Aaron and his sons shall conclude to cover the sacred [the Ark], [and all the sacred vessels…and then, the sons of Kehat shall come to bear…]” (Numbers 4:15). That is why Aaron is written in the speech regarding the sons of Kehat, as he is commanded regarding their service and their burden. But regarding the sons of Gershon, you do not find that Aaron did anything there; rather, it is under his direction the sons of Gershon would do everything that they do, and their actions were under the supervision of Itamar, as he would assign to each and every one of them his service and his burden. That is why Aaron is not written in the speech in the portion of the sons of Gershon.
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