These were the sons of Levi, after the house of their fathers,
 &c.] According to the three classes of them, as descending from the three sons of Levi: 
 [even] the chief of the fathers;
 or heads of families: 
 as they were counted by number of names by their polls;
 or according to their heads, one by one: 
 that did the work for the service of the house of the Lord;
 the particulars of which are in (  1 Chronicles 23:28-31 ) 
 from the age of twenty years, and upwards;
 they were first numbered thirty and upwards, ( 1 Chronicles 23:3 ) , but David before his death ordered they should be numbered from twenty and upwards, ( 1 Chronicles 23:27 ) , because the Israelites being increased, there would be more work for the priests in the temple, which would require the assistance of more Levites. The reasons follow.