V.1-6 Another change. The introduction of groups singing with musical instruments. Never before had this been a part of the Jewish public worship. In the days of the tabernacle, sacrifices were the main feature, but in the days of the temple — the future days of glory on earth — songs of triumph will be the main theme. However, sacrifices will be there, but they will be a memorial of Christ’s death.
V.7 “Twelve” means administrative responsibility. These men shared responsibility with David. During the millennium, angels are not going to have this place of responsibility under the Lord, as they have today. Believers will take the place the angels have now (Heb. 2:55For unto the angels hath he not put in subjection the world to come, whereof we speak. (Hebrews 2:5)). Believers during the present day of grace, who have been faithful to God will have greater rewards and responsibilities then (Luke 19:15-1915And it came to pass, that when he was returned, having received the kingdom, then he commanded these servants to be called unto him, to whom he had given the money, that he might know how much every man had gained by trading. 16Then came the first, saying, Lord, thy pound hath gained ten pounds. 17And he said unto him, Well, thou good servant: because thou hast been faithful in a very little, have thou authority over ten cities. 18And the second came, saying, Lord, thy pound hath gained five pounds. 19And he said likewise to him, Be thou also over five cities. (Luke 19:15‑19)) — 288 is divisible by 12 (12 Times 24).
V.8-31 All is divided into 24 (2 x 12) groups, the teachers as well as the scholars. When the Lord reigns over the earth, all will be perfectly run.