What does Psalm 35:5 mean?

David asks the Lord to drive his enemies away just as the wind drives chaff away from a threshing floor. After grain was cut down and collected, it was "threshed" to break it apart into separate components. Farmers then intentionally tossed grain into the air so the wind would blow away the inedible husks and stems—the "chaff"—and the heavier grains would remain. "Chaff" is therefore a common metaphor for something undesirable, or worthless.

Psalm 1 contrasts the righteous and the wicked, stating that the righteous are blessed and productive but the wicked "are like chaff that the wind drives away" (Psalm 1:4). John the Baptist chided the hypocritical Pharisees and Sadducees by comparing them to chaff. He proclaimed, "[Messiah's] winnowing fork is in his hand, and he will clear his threshing floor and gather his wheat into the barn, but the chaff he will burn with unquenchable fire" (Matthew 3:12). The Lord knows who belongs to Him, and someday He will gather them into heaven, but the unsaved He will drive into eternal destruction (Malachi 4:1; John 3:16–18, 36).

David sees his enemies as worthless, and he believes they are defenseless against the force of the angel of the Lord. The phrase "angel of the LORD" can refer to a specific manifestation of God, in a temporary physical form (Exodus 3:2; Judges 6:11). It can also be a general reference to one of God's spiritual messengers—angels—who enact His will (Matthew 1:24; Acts 5:19).