Eleazar shall be chief, next under the high priest; whence he is called the second priest, 2 Kings 25:18; and in case of the high priest's absence by sickness or other necessary occasions, he was to perform his work, 1 Kings 4:4; and he had a superiority over all the rest of the priests and Levites. Over the chief of the Levites, i.e. over those three persons, who were each the chief of their several families; of whom see here, Numbers 3:24,31,35.
Related Commentaries of Numbers 3:32
Numbers 3:32
32 And Eleazar the son of Aaron the priest shall be chief over the chief of the Levites, and have the oversight of them that keep the charge of the sanctuary.