Rashi on Numbers
וזר לא יקרב אליכם AND A LAYMAN SHALL NOT APPROACH UNTO YOU — It is you whom I admonish concerning this.
Sforno on Numbers
ושמרו את משמרת אהל מועד, within the curtained off area of the courtyard.
Rabbeinu Bahya
ושמרו את משמרת אהל מועד, “and they are to safeguard the duties pertaining to the Tent of Meeting.” The purpose of this שמירה, supervision, is to enhance the reputation of the Tabernacle as it is a well known fact that any building surrounded by guards of honour is considered as of greater importance by people seeing the guards than even a palace not surrounded by guards.