Matthew Poole and continuators on 1 Chronicles 15:18

18 And with them their brethren of the second degree , Zechariah, Ben, and Jaaziel, and Shemiramoth, and Jehiel, and Unni, Eliab, and Benajah, and Maasiah, and Mattithlah, and Eliphalet, and Mikniah, and Obed-edom, and Jeiel the porters .

The first rank or degree of Sacred Musicians being those three famous Persons named v. 17. next unto whom were these here named.

Who were to keep the Doors of the Tabernacle and Courts, but withal were instructed in Musick and singing, that when they were free from Attendance upon their proper Office, they might not be idle nor unprofitable persons in Gods House.