They shall wait, in their own persons, not by the Levites. The stranger, i.e. every one who is of another family than Aaron s, yea, though he be a Levite. See Numbers 1:53, Numbers 16:40. That cometh nigh, to wit, to execute any part of the priest's office.
Related Commentaries of Numbers 3:10
Numbers 3:10
10 And thou shalt appoint Aaron and his sons, and they shall wait on their priest's office: and the stranger that cometh nigh shall be put to death.