For there they that carried us away captive required of us a song; literally, words of song. The oppressors break into the retired gathering of their captives, and "require of them a song"—demand roughly and rudely to be entertained with the foreign music, which is perhaps sweeter than their own, or at any rate more of a novelty.
And they that wasted us required us mirth. Not only was "a song" wanted but a joyous song - one that would wake feelings of mirth and gladness in those who heard it. Saying, sing us one of the songs of Zion; literally, sing us frown a song of Zion.
The captives had, no doubt, spoken of the joyous strains which they had been wont to pour forth in their own city upon festive occasions. Their conquerors demand a specimen, but are repulsed with the words of the next verse.