What is the meaning of "Taharu Chashash"?
Rashi: You will become pregnant with a kind of chaff that burns easily.
Radak: It is fine straw. This applies to the nations in the camp of Melech Ashur. Intent is called pregnancy, and action is called birth. They intended to conquer Yerushalayim, but did not succeed. Their intent is folly and their act is nothing - the verse calls them chaff and straw.
Malbim: Chashash is the end of the sheave.
Why does it say "Ruchachem Esh Tochalchem"?
Rashi: From your bodies will come out a wind of fire, and consume the chaff and straw.
Radak: Your intent will be fire that will consume you. I.e. because you came to Yerushalayim and thought to conquer it, fire will consume you - this is Hashem's angel that struck Machaneh Ashur. It is called fire also above (10:16).
Malbim: Ruchachem is the speech that comes out of your mouths - your messengers' blasphemy of Hashem. This is the fire that will burn straw, i.e. your actions, and consume you.
