Matthew Henry Commentary Psalms 137:1-4

"By the rivers of Babylon, There we sat down, yea, we wept, When we remembered Zion. Upon the willows in the midst thereof We hanged up our harps. For there they that led us captive required of us songs, And they that wasted us [required of us] mirth, [saying], Sing us one of the songs of Zion. How shall we sing Jehovah`s song In a foreign land?" — Psalms 137:1-4 (ASV)

Their enemies had carried the Jews captive from their own land. To complete their woes, they mocked them; they demanded from them mirth and a song. This was very barbaric; also profane, for no songs would do except the songs of Zion. Scoffers are not to be complied with. They do not say, "How can we sing when we are in such great sorrow?" but rather, "It is the Lord's song; therefore, we dare not sing it among idolaters."