What does Psalm 129:7 mean?

"Imprecation" means wishing harm on someone. Several psalms call on the Lord to bring some hurt to an enemy, so they are labeled "imprecatory" psalms. Psalm 129 shows the typical language of those songs (Psalm 17:13; 35:4–6). Only a few (Psalm 58:6–9; 137:8–9) are truly aggressive. Here, the psalmist asks for those who hate Israel and her people (Psalm 129:5) to wither away like grass growing by accident on a roof (Psalm 129:6). Such plants would not be part of a harvest nor serve a useful purpose.

Believers are compared to sowers and reapers. They sow the gospel seed in tears but joyfully gather an abundant harvest (Psalm 126:5–6). John the Baptist warned hypocritical Pharisees and Sadducees about future judgment. He said Messiah "will clear his threshing floor and gather his wheat into the barn, but the chaff he will burn with unquenchable fire" (Matthew 3:12). Random grasses and weeds would be part of that discarded chaff.