Bel was the main god of the Babylonians and represents the whole country and the people that worshiped it. (See: [[rc://en/ta/man/translate/figs-metonymy]])
The many nations that come to Babylon to sacrifice to Bel is spoken of as a river that moves along. AT: "the people of other nations will no longer come in large groups" (See: [[rc://en/ta/man/translate/figs-metaphor]])