Matthew Poole and continuators on Numbers 18:7

7 Therefore thou and thy sons with thee shall keep your priests office for every thing of the altar , and within the vail , and ye shall serve: I have given your priests office unto you, as a service of gift : and the stranger that cometh nigh shall be put to death.

To wit, of burnt-offering, as appears from the following words.

This phrase elsewhere signifies the inward or second vail, but here it signifies either the outward vail onely, or rather both the vails, the singular number being put for the plural, as when the altar is put for both the altars, as hath been noted; and so this phrase comprehends both the holy and the most holy place.

As a gift which I have freely conferred upon you and upon you alone; and therefore let no man henceforth dare either to charge you with arrogance and usurpation in appropriating this to your selves, or to invade your office.