Because their office was to wait on the sons of Aaron. — For their appointment (or station) is at the side of the sons of Aaron (i.e., the priests). The Levites had no longer to carry the sacred dwelling and its vessels, but to minister, in subordination to the priesthood, in the permanent sanctuary.
In the courts. — Over (i.e., in charge of) the courts, and over the cells, or chambers built around the courts, in which were kept stores and treasures (1 Chronicles 9:26), and in which priests and Levites lived.
And in (over) the purifying of all holy things. — 2 Chronicles 30:19. They had to cleanse the sacred vessels and the sanctuary itself.