A Commentary, Critical, Practical, and Explanatory on the Old and New Testaments, by Robert Jamieson, A.R. Fausset and David Brown  at sacred-texts.com
1 Chronicles 25:1
ch1 25:1NUMBER AND OFFICE OF THE SINGERS. (Ch1 25:1-7)
David and the captains of the host--that is, the princes (Ch1 23:2; Ch1 24:6). It is probable that the king was attended on the occasion of arranging the singers by the same parties that are mentioned as having assisted him in regulating the order of the priests and Levites.
1 Chronicles 25:2
ch1 25:2according to the order of the king--Hebrew, "by the hands of the king," that is, "according to the king's order," under the personal superintendence of Asaph and his colleagues.
which prophesied--that is, in this connection, played with instruments. This metaphorical application of the term "prophecy" most probably originated in the practice of the prophets, who endeavored to rouse their prophetic spirit by the animating influence of music (see on Kg2 3:15). It is said that Asaph did this "according to David's order," because by royal appointment he officiated in the tabernacle on Zion (Ch1 16:37-41), while other leaders of the sacred music were stationed at Gibeon.
1 Chronicles 25:5
ch1 25:5Heman the king's seer--The title of "seer" or "prophet of David" is also given to Gad (Ch1 21:9), and to Jeduthun (Ch2 29:14-15), in the words (Margin, "matters") of God.
to lift up the horn--that is, to blow loudly in the worship of God; or perhaps it means nothing more than that he presided over the wind instruments, as Jeduthun over the harp. Heman had been appointed at first to serve at Gibeon (Ch1 16:41). But his destination seems to have been changed at a subsequent period.
God gave to Heman fourteen sons and three daughters--The daughters are mentioned, solely because from their musical taste and talents they formed part of the choir (Psa 68:25).
1 Chronicles 25:6
ch1 25:6All these were under the hands of their father--Asaph had four sons, Jeduthun six, and Heman fourteen, equal to twenty-four; making the musicians with their brethren the singers, an amount of two hundred eighty-eight. For, like the priests and Levites, they were divided into twenty-four courses of twelve men each, equal to two hundred eighty-eight, who served a week in rotation; and these, half of whom officiated every week with a proportionate number of assistants, were skilful and experienced musicians, capable of leading and instructing the general musical corps, which comprised no less than four thousand (Ch1 23:5).
1 Chronicles 25:8
ch1 25:8THEIR DIVISION BY LOT INTO FOUR AND TWENTY ORDERS. (1Ch. 25:8-31)
they cast lots, ward against ward--"Ward" is an old English word for "division" or "company." The lot was cast to determine the precedence of the classes or divisions over which the musical leaders presided; and, in order to secure an impartial arrangement of their order, the master and his assistants, the teacher and his scholars, in each class or company took part in this solemn casting of lots. In the first catalogue given in this chapter the courses are classed according to their employment as musicians. In the second, they are arranged in the order of their service.