A.T. Robertson Commentary Revelation 19:1

"After these things I heard as it were a great voice of a great multitude in heaven, saying, Hallelujah; Salvation, and glory, and power, belong to our God:" — Revelation 19:1 (ASV)

After these things (μετα ταυτα). Often when a turn comes in this book. But Beckwith is probably correct in seeing in 19:1-5 the climax of chapter Re 18. This first voice (verses 1,2) ως φωνην μεγαλην ουχλου πολλου (as it were great voice of much multitude) is probably the response of the angelic host (Revelation 5:11; Hebrews 12:22). There is responsive singing (grand chorus) as in chapters Re 4; 5.

Saying (λεγοντων). Present active participle of λεγω, genitive plural, though οχλου is genitive singular (collective substantive, agreement in sense).

Hallelujah (Αλληλουια). Transliteration of the Hebrew seen often in the Psalms (LXX) and in III. Macc. 7:13, in N.T. only in Re 19:1,3,4,6. It means, "Praise ye the Lord." Fifteen of the Psalms begin or end with this word. The Great Hallel (a title for Ps 104-109) is sung chiefly at the feasts of the passover and tabernacles. This psalm of praise uses language already in 12:10.