Declare ... among ... nations - who would rejoice at the fall of Babylon their oppressor.
standard - to indicate the place of meeting to the nations where they were to hear the good news of Babylon’s fall [Rosenmuller]; or, the signal to summon the nations together against Babylon (Jer 51:12, Jer 51:27), [Maurer].
Bel - the tutelary god of Babylon; the same idol as the Phoenician Baal, that is, lord, the sun (Isa 46:1).
confounded - because unable to defend the city under their protection.
Merodach - another Babylonian idol; meaning in Syria “little lord”; from which Merodach-baladan took his name.