Barnes' Notes on the Whole Bible

The actual lighting of the lamps (compare the marginal references) was to be done to set forth symbolically the special presence which God had now Numbers 7:89 actually established among His people.

Were purified - Rather, purified themselves; as directed in Numbers 8:7.

Twenty and five years old and upward - The permanent limit as distinguished from the temporary Numbers 4:3, Numbers 4:23, Numbers 4:30, though David found it necessary to extend the period of the Levites’ service by causing it to commence at 20 years of age 1 Chronicles 23:24-28. This rule continued in force from the time of David downward (compare on 2 Chronicles 31:17; Ezra 3:8).