1 Chronicles 25
Like the priests and the Levites, the singers were divided by lot, designated by God's free choice. Nothing was left to the will of man: that is of all importance. The Lord's Anointed orders and the Lord decides. As for the Levites, here lots are cast for their charges, "the small as well as the great, the teacher with the scholar" (1 Chron. 25:8).
Moreover, it is under the king's direction that Asaph; Heman, David's seer in the words of God; and Jeduthun prophesy with sacred instruments — whether it be to celebrate and praise the Lord, or whether it be to exalt His power. This is one proof, among many others, that the Psalms are an inspired collection, whose character is prophetic.
In 1 Chron. 25:9-31 we find the different courses of singers chosen by lot and in connection with their three leaders. Asaph has only four courses of twelve men each. Jeduthun has six courses, Heman has fourteen; in all twenty-four courses composed of 288 persons. They correspond to the courses of the priesthood. Heman, "the king's seer in the words of God, to exalt his power," has the largest number of sons. His functions correspond to the glory of the kingdom, announced by prophecy and established by the word of God.