Their duties were the ark, the table, the lampstand, the altars, the articles of the sanctuary used with them, and the curtain—all the service for these items.
The Levites being granted to Aaron to minister to him, they are here delivered to him by tale, that he might know what he had, and employ them accordingly. Observe, I. By what rule they were numbered: Every male from a month old and upward, Num 3:15.
Commenting on Numbers 3:14-39
And Eleazar the son of Aaron the priest,.... Who was of the first of these families, the Amramites: shall be chief over the chief of the Levites; over the three chiefs of the three houses of the Levites, who were Eliasaph the son of Lael, the chief of the Gershonites; and Elizaphan the son of Uzziel, the chief of the Kohathites; and Zuriel the son...
And their charge [shall be] the ark, and the table, and the candlestick, and the altars, and the vessels of the sanctuary wherewith they minister, and the hanging, and all the service thereof. (l) The main things within the sanctuary were committed to the Kohathites.