וְנִלְו֣וּ עָלֶ֔יךָ וְשָֽׁמְר֗וּ אֶת־מִשְׁמֶ֙רֶת֙ אֹ֣הֶל מוֹעֵ֔ד לְכֹ֖ל עֲבֹדַ֣ת הָאֹ֑הֶל וְזָ֖ר לֹא־יִקְרַ֥ב אֲלֵיכֶֽם׃
And they shall be joined unto thee, and keep the charge of the tent of meeting, whatsoever the service of the Tent may be; but a common man shall not draw nigh unto you.
Read kabbalistic (mystical) interpretation of Numbers 18:4: and classical mystical sources.