Or HaChaim on Numbers 16:3/אור החיים על במדבר ט״ז:ג׳

1 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.

2In view of this, מדוע תתנשאו "why do you raise yourselves above the community of G'd?" Korach and company referred specifically to the domain of the Tabernacle and the Sanctuary which Moses had declared out of bounds to ordinary Israelites on pain of death. They accused Moses and Aaron of having insulted the community as a whole by denying them access to the Sanctuary and the opportunity to perform sacrificial service there.