en_tn_condensed/jer/50/42.md

They will pick up bows and spears

"The soldiers will carry bows and spears"

Their sound is like the sea roar

The loud noise that the soldiers make is compared to the loud noise of the sea. Alternate translation: "The sound that they make is very loud, like the sound of the sea" (See: rc://en/ta/man/jit/figs-simile)

they are riding on horses, set out in order as men for battle

The phrase "set out in order" means that they have organized themselves and are riding in rows. The phrase "as men for battle" indicates that they are ready to fight. Alternate translation: "they are riding on horses in their assigned rows, and they are ready to fight"

daughter of Babylon

This phrase refers to the Babylonian people. (See: rc://en/ta/man/jit/figs-metonymy)