Rashi on Tanakh1 Chronicles 25

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.”

and Mattithiah - six But you will find only five. [The answer is that] his wife was pregnant with Shimei, and he saw through the holy spirit that he too was destined to be the chief of a watch; therefore he says “six.” And that is what is stated further: (verse 17): “The tenth: Shimei.” This is what the liturgical poet set down (in the Kedushah of Yozer of Parashath Shekalim): “Inscribed from the womb to be counted in the watch of the Sanctuary.”

beside their father Jeduthun עַל יְדֵי, similar to (Neh. 3:8): “And beside him (עַל יָדוֹ)... repaired.”

who prophesied with [songs of] thanksgiving and praise For on the harp they would play songs of “Give thanks (הוֹדוּ)” and songs of “Hallelujah (הַלְלוּיָהּ),” and he would prophesy.

and Romamti Ezer This is one name.

the king’s seer, in words of God to raise the horn the horn of the prophecy, for he would prophesy for the king. A similar instance of this is (I Sam. 2:10): “... and raise the horn of His anointed one.”

and God gave Heman Had not God given him children, it would have been impossible for him to have fourteen sons and three daughters, with all of them fit to be chiefs of watches. A similar case is (Ruth 4:13): “... and the Lord gave her conception, and she bore a son.” Had not this been a gift from the Lord, it would have been impossible for Boaz to father a son, because he was old. Similarly, (Deut. 34:1): “and the Lord showed him all the land.” Had this vision not been from the Lord, it would have been impossible to see so far.

every expert - Heb. הַמֵּבִין. In regard to song, the expression is appropriate, for it is written: (below verse 8): “expert (מֵבִין) with pupil.” [Also] (15:22): “And Chenaniah, the leader of the Levites in song; he would chastise in song because he was an expert (מֵבִין).”

And they cast lots, a watch against The meaning is a watch against a watch, and a similar [case] is [found] above (16:5): “... but I have walked from tent to tent and from tabernacle,” which means: “and from tabernacle to tabernacle.”

like the small one so the great one, scholar with pupil The meaning is that they cast lots for the watches, this one against that one, a watch against a watch, the small one was like the great one, the expert master with the pupil, all of them were equal in this, for the one on whom the first lot fell, if to the small one, he would come first to be the first one, and if last, he would be the last one, and so all of them, whether a scholar or a pupil, whether a small person or a great one. And these watches of the Levites followed the watches of the priests: the one to whom the first lot fell had the first lot, and his watch was with the watch of Jehoiarib the priest, and the one to whom the second lot fell waited, and his watch was with the watch of Jedaiah the priest.

And the first lot of Asaph came out to Joseph his first son.

Gedaliah the second Gedaliah was the firstborn of Jeduthun.

he and his brethren and his sons, twelve The meaning is that for every watch twelve Levites would come, for all of them equalled two hundred and eighty-eight, and if you divide them into twenty-four parts, each part will consist of twelve Levites. So it appears to me. And this is the meaning of “and his brethren and his sons”: referring to Joseph and to Gedaliah. And since they are both mentioned in one verse, he wrote only once, “he and his sons and his brethren.” And not every “his brethren,” and “their brethren” in this context mean his actual brothers; but he calls one group brethren (in German, Bruderschaft).

The third: Zaccur the firstborn of Asaph.

The fourth to Izri the second son of Jeduthun.

The fifth: Nethaniah the third son of Asaph. So the lot fell from this one to that one.