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 loud 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 God" or "Let us praise God." See how you translated this in Revelation 19:1.

For the Lord

"Because the Lord"