פְּקֹד֙ אֶת־בְּנֵ֣י לֵוִ֔י לְבֵ֥ית אֲבֹתָ֖ם לְמִשְׁפְּחֹתָ֑ם כָּל־זָכָ֛ר מִבֶּן־חֹ֥דֶשׁ וָמַ֖עְלָה תִּפְקְדֵֽם׃
’Number the children of Levi by their fathers’houses, by their families; every male from a month old and upward shalt thou number them.’
Read kabbalistic (mystical) interpretation of Numbers 3:15: and classical mystical sources.