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).