en_tn_condensed/rev/19/06.md

Then I heard what sounded like the voice of a great number of people, like the roar of many waters, and like mighty crashes of thunder

John speaks of what he is hearing as if it were like the sound made by a very large crowd of people, a large body of rushing water, and very loud thunder. (See: rc://en/ta/man/jit/figs-simile)

Hallelujah

This word means "Praise Yahweh." Some modern versions translate it as "Praise the Lord." See how you translated this in Revelation 19:1.

For the Lord

"Because the Lord"