The Numbering of the Levites
In the wilderness of Sinai, the LORD tells Moses to count the Levites by family, including every male a month old or more. Moses carries out the command as given.
T14hen the LORD spoke to Moses in the Wilderness of Sinai, saying, 15“Number the Levites by their families and clans. You are to count every male a month old or more.” 16So Moses numbered them according to the word of the LORD, as he had been commanded.
The three sons of Levi are named, and each line's clans are listed in turn: Gershon, Kohath, and Merari. The tribe's internal structure is laid out before their separate assignments appear.
17These were the sons of Levi by name: Gershon, Kohath, and Merari. 18These were the names of the sons of Gershon by their clans: Libni and Shimei. 19The sons of Kohath by their clans were Amram, Izhar, Hebron, and Uzziel. 20And the sons of Merari by their clans were Mahli and Mushi. These were the clans of the Levites, according to their families.