en_tn_condensed/isa/09/18.md

Wickedness burns like a fire; it devours the briers and thorns; it even burns the thickets of the forest

The people's evil deeds are spoken of as if they were a very destructive fire. This fire burns even the briers and thorns, plants that grow in places where people no longer live, and "the thickets of the forest" where no one has ever lived, because it has already destroyed the places where people were living. (See: rc://en/ta/man/translate/figs-metaphor)

briers ... thorns

The words "briers" and "thorns" both refer to useless, thorny plants; they can be translated using one word. See how you translated these words in Isaiah 7:23. Alternate translation: "thorn bushes" (See: rc://en/ta/man/translate/figs-doublet)