Music has spiritual power, as well as the ability to affect our minds and our bodies. Not only was music in the Old Testament used for worship, it also participated in warfare on occasion. Their songs were not pleas for help, nor were they songs extoling their own prowess. The songs they sang praised the Lord and the beauty of holiness. When the Lord saw that the people were serious about praising Him, He won the victory for them.
Hebrew poetry takes one idea and states that idea in two different ways.
If so, this is the only passage in Scripture that indicates that angels sing. And when he had taken the book, the four beasts and four and twenty elders fell down before the Lamb, having every one of them harps, and golden vials full of odours, which are the prayers of saints. Worthy is the Lamb that was slain to receive power, and riches, and wisdom, and strength, and honour, and glory, and blessing. And every creature which is in heaven, and on the earth, and under the earth, and such as are in the sea, and all that are in them, heard I saying, Blessing, and honour, and glory, and power, be unto him that sitteth upon the throne, and unto the Lamb for ever and ever. And the four beasts said, Amen.