What does Psalm 137:4 mean?

The people of Israel were carried into captivity by Babylon (2 Chronicles 36:17–21). The people are depicted as mourning by canals and setting aside their instruments in sorrow (Psalm 137:1–2). Adding insult to injury, the Babylonian abductors mock the Israelites, asking them to sing about their homeland (Psalm 137:3) of Zion—another name for Jerusalem (2 Samuel 5:7; 1 Kings 8:1).

Beyond the misery of being captives, being asked to sing songs about Zion was a stinging reminder of why Israel was in this situation. Many of "the LORD'S songs" celebrated God's protection (Psalm 9:3–6; 44:7–8; 76:1–3). Yet the Lord also told Israel that if they rejected or disobeyed Him, they would be taken into exile (Deuteronomy 28:1, 64; Jeremiah 29:10–14). It would have been difficult to sing those familiar songs knowing that Jerusalem was destroyed and the people were exiled—on account of their own sin.

There is probably an element of resistance here, as well. The request to sing is not sincere; it's about ridicule. Performing songs about the glory of God so that others can mock them is not honoring to the Lord. The purpose of praise and worship is not entertainment (Colossians 3:16). The captives probably had the sense that singing godly songs to pagan captors would be a waste of time (Matthew 7:6).