וְהַֽעֲמַדְתָּ֙ אֶת־הַלְוִיִּ֔ם לִפְנֵ֥י אַהֲרֹ֖ן וְלִפְנֵ֣י בָנָ֑יו וְהֵנַפְתָּ֥ אֹתָ֛ם תְּנוּפָ֖ה לַֽיהוָֽה׃
And thou shalt set the Levites before Aaron, and before his sons, and offer them for a wave-offering unto the LORD.
Read midrashic interpretation of Numbers 8:13: and classical rabbinic exegesis.