O daughter of Babylon, who art to be destroyed; happy shall he be, that rewardeth thee as thou hast served us.
O daughter of Babylon, who art to be destroyed - literally, 'who art destroyed.;' i:e., who art surely doomed to destruction (cf. the same idiom, Psalms 18:3). Orosius said, 'It seemed almost incredible to mortals that Babylon could have been built by human toil, or, that it could be destroyed by human valour.' Yet so it came to pass, because God had said it. "Daughter of Babylon" (cf. 2 Kings 19:21). Cities are often represented as virgins.
Happy (shall he be) that rewardeth thee as thou hast served us - literally, 'that shall repay to thee thy deed which thou didst to us' (cf. Jeremiah 48:10).