Psalm 137:8-9, How can we sing in a foreign land?

//In my book about Revelation, I suggested that this psalm may be the both the most heartrending and the most disturbing passage in the Bible. Can you imagine being so consumed by hatred for your captors, that you dream of dashing their babies against rocks?

By the rivers of Babylon we sat and wept when we remembered Zion. There on the poplars we hung our harps, for there our captors asked us for songs, our tormentors demanded songs of joy; they said, “Sing us one of the songs of Zion!” How can we sing the songs of the LORD while in a foreign land?

This psalm provides a testament to the suffering the Jews endured through the centuries, as the Bible was being compiled. If not for such hardships, our scriptures would perhaps be lifeless.