2 Chronicles 8:14

And he appointed, according to the order of David his father, the courses of the priests to their service,.... The twenty four courses which served weekly in their turns, 1 Chronicles 24:1

and the Levites to their charges, to praise and minister before the priests, as duty of every day required; who also had their courses by lot, to sing the praises of God, when the priests sacrificed, or blew the trumpets, 1 Chronicles 25:1,

the porters also by their courses at every gate; from hence Dr. Lightfoot concludes that these were divided into twenty four classes, as the priests and Levite singers were:

for so had David the man of God commanded, 1 Chronicles 26:1, who in all these affairs acted as a prophet, under the inspiration and direction of the Holy Spirit of God.