וְאֶת־אַהֲרֹ֤ן וְאֶת־בָּנָיו֙ תִּפְקֹ֔ד וְשָׁמְר֖וּ אֶת־כְּהֻנָּתָ֑ם וְהַזָּ֥ר הַקָּרֵ֖ב יוּמָֽת׃ (פ)
And thou shalt appoint Aaron and his sons, that they may keep their priesthood; and the common man that draweth nigh shall be put to death.’
Read kabbalistic (mystical) interpretation of Numbers 3:10: and classical mystical sources.