John Gill Commentary Numbers 3:32

"And Eleazar the son of Aaron the priest shall be prince of the princes of the Levites, [and have] the oversight of them that keep the charge of the sanctuary." — Numbers 3:32 (ASV)

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 of Abihail, the chief of the Merarites:

[and have] the oversight of them that keep the charge of the
sanctuary ;
the Kohathites, who had the care of the things belonging to the holy and most holy places; and these were particularly under the inspection of Eleazar, because they were things the priests had a, special concern in; see (Numbers 4:32) .