Loose hulls separated from the edible grains by threshing and winnowing. In Bible times, winnowed grain was a common sight. The wind blew away the lighter husks, leaving only the grain. This gave rise to a strong metaphor. It symbolized that good people or nations would survive judgment, but the wicked would not. So, for example, sinners “are like chaff driven off by the wind” (Psalm 1:4).
The prophet Isaiah said of the Assyrians, “You conceive chaff; you give birth to stubble. Your breath is a fire that will consume you” (Isaiah 33:11). In Nebuchadnezzar’s dream, the world's nations collapse and are like the chaff of the summer threshing floors before the victory of the coming kingdom of God (Daniel 2:35).
In the New Testament, it is said that the coming Messiah will “gather His wheat into the barn; but He will burn up the chaff with unquenchable fire” (Matthew 3:12).