Numbers 4:29 Midrash

בְּנֵ֖י מְרָרִ֑י לְמִשְׁפְּחֹתָ֥ם לְבֵית־אֲבֹתָ֖ם תִּפְקֹ֥ד אֹתָֽם׃

As for the sons of Merari, thou shalt number them by their families, by their fathers’houses;

Read midrashic interpretation of Numbers 4:29: and classical rabbinic exegesis.