Charles Ellicott Commentary Isaiah 9:18

"For wickedness burneth as the fire; it devoureth the briers and thorns; yea, it kindleth in the thickets of the forest, and they roll upward in a column of smoke." — Isaiah 9:18 (ASV)

It shall devour the briers and thorns ... —The words are obviously figurative for men who were base and vile, as in 2 Samuel 23:6; but the figure may have been suggested by Isaiah 7:23-24. The outward desolation, with its rank growth of undergrowth, was to the prophet’s eye a type of the moral condition of his people. And for such a people sin becomes the punishment of sin, and burns like a fire in a forest thicket, leaving the land clear for fresh cultivation and a better growth. (James 3:5; Hebrews 6:8.)