John Gill Bible Commentary

And let the priests also, which come near unto the Lord,.... Either the firstborn, as the Jews generally interpret it, so Jarchi and Aben Ezra; who were sanctified to the Lord, and in whose stead afterwards the Levites were taken; or the sons of Aaron, who should be, and were potentially, though not actually priests, as Ben Gersom expresses it, from an ancient book of theirs called Mechilta; or rather some principal persons, as heads of families and the like, who, before the priesthood was settled in the family of Aaron, officiated as priests, and drew nigh to God, and offered up sacrifices for themselves and others, and were distinguished from others by this character, and therefore do not intend princes, as some interpret the word; for the description of them will not agree to them, but plainly points to a sort of men, to whom it was peculiar to perform that office. These Moses is bid to charge that they sanctify themselves; in the same manner as the people in general were before ordered, and keep themselves within the same bounds; not daring to transgress them, because they were persons that used to draw nigh to God in the performance of religious actions: lest the Lord break forth upon them; and smite them, that they die, in like manner as he made a breach on Uzzah afterwards for touching the ark of the Lord, Sa2 6:6.