One who is not a priest must not serve

"They shall be joined with you and attend to the obligations of the tent of meeting, for all the service of the tent; but an outsider may not come near you.

Hebrew

ד וְנִלְווּ עָלֶיךָ--וְשָׁמְרוּ אֶת-מִשְׁמֶרֶת אֹהֶל מוֹעֵד, לְכֹל עֲבֹדַת הָאֹהֶל; וְזָר, לֹא-יִקְרַב אֲלֵיכֶם.

Greek

4 καὶ προστεθήσονται πρὸς σὲ καὶ φυλάξονται τὰς φυλακὰς τῆς σκηνῆς τοῦ μαρτυρίου κατὰ πάσας τὰς λειτουργίας τῆς σκηνῆς, καὶ ὁ ἀλλογενὴς οὐ προσελεύσεται πρὸς σέ.

• Parashah: Korach
• Sefer HaChinuch: 390
• Mishneh Torah: Service — Entry into the Temple

• Numbers 18:4

Enumeration and classification from BibleData. The Greek is the Septuagint reading of the same verse, carried by the source for comparison.