Tafsiran Bilangan 16:3: Rashi, Sforno, Or HaChaim & Rabbeinu Bahya

רב לכם You TAKE TOO MUCH UPON YOU — i.e. much more than is proper have you taken for yourselves in the way of high Office.

ויקהלו על משה ועל אהרן, Korach, Datan and Aviram, assembled in order to incite against Moses and Aaron in the presence of 250 dignitaries of the people who had allowed themselves to be incited. This incident occurred at a time when a number of Israelites had assembled in the vicinity of Moses waiting to have their respective complaints adjudged. The 250 men mentioned walked around as if minding their own business, wanting to consult Moses about some harmless matter. It was their intention to arouse the crowd in order to provide support for Korach’s and his henchmen’s insurrection as soon as the latter would show up and begin asking hostile questions of Moses and Aaron. They selected an hour of day when there was a sizable crowd in Moses’ vicinity in order to reap the maximum benefit from that, and so that all those who were convinced of the validity of Korach’s complaints would spread the word and bring reinforcements from the plain people in the camp.

רב לכם כי כל העדה כלם קדושים, "a great deal for you, for the whole community is holy." They meant that Moses and Aaron had arrogated too much authority to themselves. In the event that Moses and Aaron would ask wherein precisely they had arrogated to themselves too much authority, Korach and company said that in view of the fact that the entire community was holy having experienced direct communication from G'd something not granted to any other nation, plus the fact that G'd remained within its midst, Moses and Aaron had placed themselves above such a holy nation. By saying ובתוכם השם, "and G'd is in their midst," they hinted that the presence of G'd was due to the people and not to the merit of Moses and Aaron.

כלם קדשים [FOR] ALL [THE CONGREGATION] ARE HOLY — they all heard the utterances on Sinai from the mouth of the Almighty (Midrash Tanchuma, Korach 4).