I Chron. 23:1-26:19
As David prepared Israel for their new king, he called a meeting of the nation’s leaders. Many years earlier, God had separated the tribe of Levi as Levites to perform the various duties of the worship assemblies. Aaron and his sons had been designated to be the priests. There were four main divisions of the responsibilities that David addressed in those closing days of his reign as king. Most of them were responsible for seeing to the work of the house of the Lord which was to be built soon. Some were officers and judges. Others were gatekeepers. Those remaining were musicians responsible for praising the Lord with musical instruments.
David was precise as he listed the various groups and leaders to perform the priestly duties. As a method of ensuring order and possibly fairness and to prevent jealousy, lots were cast to determine the times that the various priestly divisions would be responsible to serve.
After assigning the duties of the priests, David turned his attention to appointing men to be in charge of worshipping God in music. Asaph, Heman and Jeduthun had a total of twenty-four sons who were leaders of twenty-four worship groups. Each group consisted of its leader and eleven other men who were responsible for the time of their services by lot.
God made special emphasis to ensure that various individuals were responsible for playing a variety of musical instruments in worship to him. [Note that under the Christian dispensation in which we now serve, the instructions for music involve “singing and making melody in your heart to the Lord,” (Eph. 5:19). The use of mechanical instruments was omitted from Christian worship. If God had desired instruments, He would surely have given specific instructions for them as He did during the time of David.]
David assigned a special group of gatekeepers to be responsible for the security of the temple. They were identified as of the Korahites and were placed at the East Gate, North Gate, South Gate and West/Shallecheth Gate.