These were the sons of Levi after their fathers' houses, even the heads of the fathers' [houses] of those of those who were counted, in the number of names by their polls, who did the work for the service of the house of Yahweh, from twenty years old and upward.
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.