וְעָבַ֨ד הַלֵּוִ֜י ה֗וּא אֶת־עֲבֹדַת֙ אֹ֣הֶל מוֹעֵ֔ד וְהֵ֖ם יִשְׂא֣וּ עֲוֺנָ֑ם חֻקַּ֤ת עוֹלָם֙ לְדֹרֹ֣תֵיכֶ֔ם וּבְתוֹךְ֙ בְּנֵ֣י יִשְׂרָאֵ֔ל לֹ֥א יִנְחֲל֖וּ נַחֲלָֽה׃
But the Levites alone shall do the service of the tent of meeting, and they shall bear their iniquity; it shall be a statute for ever throughout your generations, and among the children of Israel they shall have no inheritance.
Read midrashic interpretation of Numbers 18:23: and classical rabbinic exegesis.