O daughter of Babylon, who art to be destroyed; happy shall he be, that rewardeth thee as thou hast served us.
Babylon means the kingdom, not the city. The Jews gathered by the rivers where they could worship in the open air, since they had no synagogues there. This is history written as it happened, not prophecy: the captivity has come, and the Psalmist speaks for the whole Church under this affliction.
AI summary
Commenting on Psalm 137:1-9
O daughter of Babylon, who art to be destroyed. Or the destroyer: let us accept the word either way, or both ways: the destroyer would be destroyed, and the Psalmist in vision saw her as already destroyed. It is usual to speak of a city as a virgin daughter. Babylon was in her prime and beauty, but she was already doomed for her crimes.
The pious Jews in Babylon, having afflicted themselves with the thoughts of the ruins of Jerusalem, here please themselves with the prospect of the ruin of her impenitent implacable enemies; but this not from a spirit of revenge, but from a holy zeal for the glory of God and the honour of his kingdom. I.
Commenting on Psalm 137:7-9