Adam Clarke on Numbers 16:3

Ye take too much upon you - The original is simply רב לכם rab lachem, too much for you. The spirit of this saying appears to me to be the following: - "Holy offices are not equally distributed: you arrogate to yourselves the most important ones, as if your superior holiness entitled you alone to them; whereas all the congregation are holy, and have an equal right with you to be employed in the most holy services." Moses retorts this saying Num 16:7 : Ye take too much upon you, רב לכם rab lachem; Ye have too much already, ye sons of Levi; i.e., by your present spirit and disposition you prove yourselves to be wholly unworthy of any spiritual employment.