John had mentioned harps already in Revelation 5:8 as the heavenly instrument the twenty-four elders were playing. The term translated as “harp” denotes a small string instrument held in the hand and plucked to make sound. In the temple Solomon built on Mount Zion, Levites used this instrument to accompany the singing (1 Chronicles 25:1, 1 Chronicles 25:6; see also Psalm 33:2; Psalm 71:22; Psalm 98:5).The music John hears from heaven is the kind of sound that characterized the Old Testament temple as the Levites led the people in songs of praise for God their Saviour.
2 And I heard a voice from heaven like the roar of many waters and like the sound of loud thunder. The voice I heard was like the sound of harpists playing on their harps,