For what Avodah were they separated?
'Rashi': It was for Shir.
Are these the only ones that David separated?
'Rashi': Yes.
Radak: He separated Bnei Asaf, Yedusun and Heiman to be singers, others to be gatekeepers, and others to be Gizbarim on storehouses of Beis Hashem, like it says below.
What are "Sarei ha'Tzava la'Avodah"?
Malbim: The officers over the legions special for Avodah, like "Kol ha'Ba la'Tzava La'avod Avodah b'Ohel Mo'ed."
Why does it say "ha'Nibe'im"?
'Rashi': When they played the Shirim with these instruments, they had Nevu'ah. So it says about Elisha "v'Hayah k'Nagen ha'Meganen va'Tehi Alav Yad Hashem."
Radak: Bnei Asaf played instruments, and he had Ru'ach ha'Kodesh, and sang with the harps. The same applies to Yedusun and Heiman. Sefer Tehilim was said with Ru'ach ha'Kodesh; it has Nevu'os about Galus and Ge'ulah.
Malbim: The Shir is called Nevu'ah, for they say elevated, Divine matters.
What is the meaning of "va'Yhi Mishparam Anshei Melachah la'Avodasam"?
'Rashi': The 24 Mishmaros - four were from Bnei Asaf (verse 2), six from Yedusun (3), and 14 from Heiman (5). Below (7) gives the total number (288 Leviyim).
Malbim: Their number was like the amount needed. There must be 12 Leviyim on the Duchan for vocal Shir, and also 12 for instruments - at least two with lyres, nine with harps and one with cymbals (Erchin 10a, 13a-b 1 ).
The Mishnah said also at least two trumpets. Malbim holds that this does not discuss Leviyim playing for Shir. (PF)
