Charles H. Spurgeon on Psalms 137:8

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. Happy shall he be that rewardeth thee as thou hast served us. The avenger would be fulfilling an honourable calling in overthrowing a power so brutal, so inhuman. Assyrian and Chaldean armies had been boastfully brutal in their conquests; it was meet that their conduct should be measured back into their own bosoms. No awards of punishment can be more unanswerably just than those which closely follow the lex talionis, even to the letter. Babylon must fall, as she caused Jerusalem to fall; and her sack and slaughter must be such as she appointed for other cities. The patriot poet sitting sorrowfully in his exile, finds a solace in the prospect of the overthrow of the empress city which holds him in bondage, and he accounts Cyrus right happy to be ordained to such a righteous work. The whole earth would bless the conqueror for ridding the nations of a tyrant; future generations would call him blessed for enabling men to breathe again, and for once more making liberty possible upon the earth. We may rest assured that every unrighteous power is doomed to destruction, and that from the throne of God justice will be measured out to all whose law is force, whose rule is selfishness, and whose policy is oppression. Happy is the man who shall help in the overthrow of the spiritual Babylon, which, despite its riches and power, is "to be destroyed." Happier still shall he be who shall see it sink like a millstone in the flood, never to rise again. What that spiritual Babylon is none need enquire. There is but one city upon earth which can answer to the name.