## tongue of fire ##

"flame of fire" or "flame"

## as the tongue of fire devours stubble, and as the dry grass goes down in flame ##

These phrases mean basically the same thing. God will punish the people described in 5:18-23 as  a fire that completely and easily burns up dead grass.  Alternate translation: "as a fire burns up stubble and grass" (See: [[rc://en/ta/man/translate/figs-parallelism]] and [[rc://en/ta/man/translate/figs-simile]])

## stubble ##

"dry grain stalks." This refers to the part of the plant that is left in the garden to die after the farmer collects the food.

## their root will rot, and their blossom will blow away like dust ##

Isaiah compares those people to a dying plant. Alternate translation: "they will die like a plant whose roots have rotted and whose blossom has dried up and blown away in the wind" (See: [[rc://en/ta/man/translate/figs-metaphor]])