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.
The Gargantuan significance of this chapter lies in the proof that during the life of David king of Israel, all of the extensive instructions and details written in the Book of Moses (The Pentateuch) were well known in Israel.  As any good reference Bible will demonstrate, there is hardly a line in this chapter that does not tie in specifically with instructions in the Pentateuch.  Furthermore, all of these instructions (except David's use of instruments of music) were ancient, dating back to the times of Moses. They were not invented by David but honored by him.