Why does it say "Lachen"?
Radak: It is because he did not think that there is a Supreme One who conducts him, rather, he said that he accomplished with his strength and Chachmah. Therefore, Hashem will show him that He is the Master. He is Hashem Tzevakos - the Master of legions above and below, and He will send a plague in his troops.
What is "Razon [b'Mishmanav]"?
Radak #1: Razon is death, like "va'Yashlach Razon b'Nafsham" (Tehilim 106:15).
Radak: Because it said "b'Mishmanav" (his great healthy Giborim), it says Razon (thinness). This is like "va'Yachched Kol Gibor Chayil v'Nagid" (Divrei ha'Yamim II, 32:21). Every stout Gibor is called so - "Kol Shamen v'Chol Ish Chayil" (Shoftim 3:29), "va'Yaharog b'Mishmaneihem u'Vachurei Yisrael Hichri'a" (Tehilim 78:31).
Malbim: The glory of a kingdom depends on two matters. (a) Inner strength - Gevurah of Giborim, and courage of the masses. (b) external honor - a multitude of people and wealth. The kingdom is depicted as an individual; also his honor depends on these two things. (a) Inner strength, that he is stout and strong. (b) External honor - wealth and many children. The verse compares the fall of Sancheriv's camp, that first their inner strength and courage were destroyed. The verse depicts that a stout Gibor became thin due to himself, and not due to external illness that thins a person amidst weakness of the stomach and powere of digestion. Also refer to 10:16:4:2
What is "v'Sachas Kevodo [Yekad Yekod ki'Kod Esh]"?
Rashi, based on Sanhedrin 94a #1: [The bodies of Sancheriv's army, which are] under their Kavod (garments 1 ), were burned. Kavod refers to garments, which are Mechabed (honor) a person. Refer to 10:18:2:1.
Sanhedrin 94a #2: In place of their actual Kavod (bodies, which were burned, will be ashes).
Sanhedrin 94a #3: (Their Neshamos, which are) under their actual Kavod (bodies) were burned, like the death of Nadav and Avihu. Just like there, their Neshamos were burned, but their bodies were intact, also here.
Radak: In the place where his great awesome Machaneh was honored, fire will burn - a plague that burns like fire.
Rashi citing Midrash Agadah Bereishis 58:9: Here, Bnei Shem were paid for the honor that he did for his father when he covered his Ervah - "va'Yikach Shem va'Yefes
What do we learn from "Yekad Yekod ki'Kod Esh"?
Rashi: He will burn, like a fire.
Malbim: The Bitul of external honor will be via an external cause, like a fire that burned one's property. The verse depicts that fire from Shamayim consumed his camp. It seems from Chazal that first Yir'as Hashem fell on them, and they killed each other, and afterwards Heavenly fire burned them.
