Musar for Numbers 16:10
וַיַּקְרֵב֙ אֹֽתְךָ֔ וְאֶת־כָּל־אַחֶ֥יךָ בְנֵי־לֵוִ֖י אִתָּ֑ךְ וּבִקַּשְׁתֶּ֖ם גַּם־כְּהֻנָּֽה׃
and that He hath brought thee near, and all thy brethren the sons of Levi with thee? and will ye seek the priesthood also?
Mesilat Yesharim
What caused the destruction of Korach and his assembly? Only honor as scripture states explicitly: "do you also seek the priesthood?" (Bamidbar 16:10). Our sages told us that all this grew out of Korach's seeing Elitzafan ben Uziel promoted to head of the tribe, and he wanted to be head in his place (Bamidbar Rabbah 18:2).
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