Albert Barnes Commentary Isaiah 33:12

"And the peoples shall be as the burnings of lime, as thorns cut down, that are burned in the fire." — Isaiah 33:12 (ASV)

And the people – In the army of Sennacherib.

As the burnings of lime – As if placed in a burning lime-kiln, where they must certainly be destroyed .

As thorns cut up – As thorns, or small brushwood, that has been long cut up and perfectly dried are speedily consumed, so it will be with the Assyrian army. This is an image like many that are employed, denoting that the destruction of the army of the Assyrians would be sudden and entire.