I'm trying to imagine this. The enemy, who has captured us, wants to hear some of our songs. I can only think of those films where African-American slaves were singing in the fields while the white plantation owners romanticized our ancestor's ability to carry a tune. The nearest equivalent I can think of are rock stars using gospel choirs as backup singers...and usually in songs that have nothing to do with the gospel.
In this hymn, the psalmist describes a situation which is not readily understood by those who have not been oppressed. They oppressors like our tunes and they want to hear it. Now, whether this is a genuine liking of Israel's songs or a way to mock is unclear. The Israelites are now surrounded by their enemies. Why should they sing the Lord's song in a strange land?
The oppressors are demanding mirth and forced happiness from those they oppress. And yet...they that hold them captives don't know the power of their songs.
This request from the captors creates a psalm that ends like the other imprecatory psalms. Imprecatory psalms offend people who think anger, vengeance and spite are unspiritual. But have these offended people seen their little ones dashed to pieces by an enemy? People often judge what they don't understand.
The writer of Psalm 137 merely wishes that his enemies receive the same punishment they have given. This is a sad psalm, and for me, the sadness is even greater because the oppressors have asked the oppressed for entertainment.
1By the rivers of Babylon, there we sat down, yea, we wept, when we remembered Zion.
2We hanged our harps upon the willows in the midst thereof.
3For there they that carried us away captive required of us a song; and they that wasted us required of us mirth, saying, Sing us one of the songs of Zion.
4How shall we sing the LORD's song in a strange land?
5If I forget thee, O Jerusalem, let my right hand forget her cunning.
6If I do not remember thee, let my tongue cleave to the roof of my mouth; if I prefer not Jerusalem above my chief joy.
7Remember, O LORD, the children of Edom in the day of Jerusalem; who said, Rase it, rase it, even to the foundation thereof.
8O daughter of Babylon, who art to be destroyed; happy shall he be, that rewardeth thee as thou hast served us.
9Happy shall he be, that taketh and dasheth thy little ones against the stones.