The stranger — That is, every one who is of another family than Aaron's; yea, though he be a Levite. That cometh nigh — 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.