A.T. Robertson Commentary Revelation 14:2

"And I heard a voice from heaven, as the voice of many waters, and as the voice of a great thunder: and the voice which I heard [was] as [the voice] of harpers harping with their harps:" — Revelation 14:2 (ASV)

As a voice of many waters (ως φωνην υδατων πολλων). For which see 1:15.Of a great thunder (βροντης μεγαλης). For which see 6:1; 19:6. For this voice out of heaven see 10:4; 14:15; 18:4 and note accusative with ηκουσα.

As the voice of harpers harping with their harps (ως κιθαρωιδων κιθαριζοντων εν ταις κιθαραις αυτων). Triple use of κιθαρα (5:8), κιθαρωιδων (18:22), κιθαριζοντων (old verb κιθαριζω, in N.T. only here and 1 Corinthians 14:7). Wonderful melody in this chorus by the angels, not by the 144,000.