Numbers 16:1,2

Now Korah, the son of Izhar, the son of Kohath, the son of Levi, and Dathan and Abiram, the sons of Eliab, and On, the son of Peleth, sons of Reuben, took men:

Now Korah, the son of Izhar. Izhar, brother of Amram (Exodus 6:18), was the second son of Kohath, and for some reason unrecorded he had been supplanted by a descendant of the fourth son of Kohath, who was appointed prince or chief of the Kohathites (Numbers 3:30). Discontent with the preferment over him of a younger relative was probably the originating cause of this seditious movement on the part of Korah.

Dathan ... Abiram ... and On. These were confederate leaders in the rebellion; but On seems to have afterward withdrawn from the conspiracy.

Took men. The latter-mentioned individuals, being all sons of Reuben, the oldest of Jacob's family, had been stimulated to this insurrection on the pretext that Moses had, by an arbitrary arrangement, taken away the right of primogeniture, which had vested the hereditary dignity of the priesthood in the firstborn of every family, with a view of transferring the hereditary exercise of the sacred functions to a particular branch of his own house; and that this gross instance of partiality to his own relations, to the permanent detriment of others, was a sufficient ground for refusing allegiance to his government. In addition to this grievance, another cause of jealousy and dissatisfaction that rankled in the breasts of the Reubenites was the advancement of Judah to the leadership among the tribes. These malcontents had been incited by the artful representations of Korah (Jude 1:11), with whom the position of their camp on the south side afforded them facilities of frequent contact, and who, in addition to his feeling of personal wrongs, participated in their desire, if he did not originate the attempt, to recover their lost rights of primogeniture.

When the conspiracy was ripe, they openly and boldly declared its object, and, at the head of 250 princes, challenged Moses with an ambitious and unwarrantable usurpation of authority, especially in the appropriation of the priesthood; because they disputed the claim of Aaron also to pre-eminence. х nªsiy'eey (H5387) `eedaah (H5712) qªri'eey (H7148) mow`eed (H4150), princes or chiefs of the congregation (community) that are called to the convention (see the note at Numbers 1:16).] 'I notice this passage particularly,' says Michaelis, 'because it appears from it that 250 persons of this description, who rose up against Moses, became to him objects of terror, which they could not have been, if their voices had not been at the same time the voices of their families and tribes' (cf. Deuteronomy 29:9).