What is "Ohr Yisrael"?
Rashi: The Torah that Chizkiyah engaged in. It will be fire for Sancheriv.
Radak: It is Kel. He is Yisrael's light, and illuminates for them in the darkness that they were in - "ha'Am ha'Holechim ba'Choshech Ra'u Ohr Gadol" (9:1). Hashem is like light that illuminates and consumes. He illuminates for Yisrael, and consumes Machaneh Ashur.
Malbim: It is the time for Yisrael's salvation 1 - the end of the night "Ki Yevatza Hashem Es Ma'asehu" (12) - "v'Hayah Or Yisrael", the light of dawn that came to illuminate the night for Yisrael, was fire for Sancheriv, to burn him.
Malbim: The salvation of Am Hashem depends on two matters. (a) Time. Every affliction has a limited duration. When the time passes, it must depart, just like night departs when dawn comes. (b) Improving their deeds. Sin is the reason for the punishment. If they improve their deeds and the reason goes away, the result must go away, and they will be saved before the time. Both of these happened regarding Sancheriv. Also refer to 10:17:2:3.
What is "Kedosho [l'Lehavah]"?
Rashi #1: It is Hashem. Radak - The matter is repeated in different words.
Rashi #2: It is Tzadikim in the generation.
Malbim: Hashem is called Kedosho, based on the Kedushah and Taharah of Yisrael's deeds. He will be a flame, which is greater than fire. It burns and is seen from afar.
Why does it say "u'Va'arah v'Achlah"?
What are "Shiso u'Shmiro"?
Rashi, from Targum Yonasan: [Chizkiyah's] officers and Giborim. Radak - the great officers are called thorns, for they pained the world like thorns.
Malbim: It is a metaphor for Sancheriv's camp.
