Numbers 16:1,2

The many ample testimonies, nay, the astonishing miracles, whereby God had established the authority of Moses as chief governor, and of Aaron and his family as priests, were not sufficient to restrain the ambition of mutinous and designing men. Korah, cousin-german to Moses and Aaron, a man of some note among the Levites, thinking himself undervalued, it seems, by the post he was in as a mere Levite, and being left without hopes of arriving at the priesthood, as things now stood, resolves upon a mutiny against them, and attempts to raise himself to the priesthood, by forcing them to change their measures, or else putting them down from their authority. Sons of Reuben These are drawn into confederacy with Korah, partly because they were his next neighbours, both being encamped on the south side, partly in hopes to recover their rights of primogeniture, in which the priesthood was comprehended, which was given away from their father. Rose up That is, conspired together, and put their design in execution; before Moses Not obscurely, but openly and boldly, not fearing nor regarding the presence of Moses.