O Daughter of Babylon, doomed to destruction,
happy is he who repays you
for what you have done to us -
he who seizes your infants
and dashes them against the rocks.
These verses are the psalmist's honest expression of anger towards the Babylonians. Psalm 137 was written after the Babylonian siege of Jerusalem (Ps 137:1-4). The siege resulted in a famine in Jerusalem so severe that many people resorted to cannibalism (Lam 4:9-10). When the siege ended, the Babylonians slew many of the Israelites, blinded the king, burned the city (Jer 39:6-9), raped the women and forced the survivors into hard labor (Lam 5:4-13).
How seriously should the psalmist's expression be taken? If the Israelites had avenged themselves on the Babylonians, they would have been violating God's command (Lev 19:18) and likely would have been punished just as other vengeful nations were (Ezek 25:12-16). Interestingly, Walter C. Kaiser Jr. says in Hard Sayings of the Bible that there were no rocks or cliffs in Babylon with which the psalmist's curse could be carried out, which is an indication that he was using a figure of speech to express his anger and desire for justice.
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