Adam Clarke on Job 21:18

They are as stubble before the wind - "His fan is in his hand; he will thoroughly cleanse his floor, and the chaff he will burn with unquenchable fire. Therefore the wicked shall not stand in the judgment, but shall be like the chaff which the wind driveth away." Were not this a common thought, I should have supposed that the author of this book borrowed it from Psa 1:4. The original signifies that they shall be carried away by a furious storm; and borne off as booty is by the swift-riding robbers of the desert, who make a sudden irruption, and then set off at full speed with their prey.