פירוש על דברי הימים א 25:1

Then David separated for the service to sing the songs.

the sons of Asaph, etc. Out of all the Levites he separated only the sons of Asaph, etc.

Heman, and Jeduthun, who prophesied When they would play these musical instruments, they would prophesy. A similar incident [is told] of Elisha: (II Kings 3:15): “’And now fetch me a musician.’ And when the musician played, the hand of the Lord came upon him.”

and the number of those men expert in their work... was: i.e., There were twenty- four watches, corresponding to the twenty-four watches [of the priests (Moharich)]: viz. the four sons of Asaph, the six of Jeduthun, and the fourteen of Heman, totaling twenty-four. Below, he sums them all up, as it is written (verse 7): “And their number with their brethren, etc.”