Numbers 3:20
And the sons of Merari by their families; Mahli, and Mushi. These are the families of the Levites according to the house of their fathers. And the sons of Merari by their families; Mahli, and Mushi. These are the families of the Levites according to the house of their fathers.
Mahli and Mushi were the sons of Merari, and their names designate the family heads of the Merarite Levites counted according to ancestral households. The families of Merari thus stood among the families of the Levites organized by the house of their fathers. So organized, the Levites had assigned duties to be followed in carrying the sanctuary and its sacred objects. Their work was distinct from the sanctuary duties belonging to the priests.
That arrangement belonged to the order written in the book of Moses for appointing the priests in their divisions and the Levites in their courses for the service of God at Jerusalem, an order restored at the dedication of the second temple. The chapter stands as part of the account of the Aaronic priesthood assigned by law to the tribe of Levi for that age, until the type met its antitype.