Why does it say "Lo Ish" and "Lo Adam"?
Radak: The angel [who killed Machaneh Ashur] is not an Ish, and not an Adam.
Malbim: It will only be via Hashem. Sometimes Hashem fells the enemy, and afterwards human swords consume the enemy, like in most wars of Yisrael. Hashem felled the enemy in front of Yisrael, and Yisrael destroyed them via the sword. "Ish" includes angels; Hashem Himself killed them, and then the angel's sword consumed them 1 . An angel is not 'Adam'.
This is like the opinion (in Sanhedrin 94a) that the bodies of Sancheriv's army were burned. The angel's sword was red-hot, or miraculously burned them. The other opinion holds that their bodies remained intact! (PF)
It said that there will not be a sword. Why does it say "v'Nas Lo Mipnei Cherev"?
Radak: Melech Ashur will flee as if from a sword - as if men bearing swords chase him. When he sees the great plague in his camp, he will flee.
Malbim: One who falls via Hashem, he need not flee afterwards when the danger departs, and he need not pay a tax. However, the plague [in Machaneh Ashur] was due to Chizkiyah and his nation, so they needed to flee Chizkiyah's sword and pay taxes.
Who are "Bachurav"?
Radak: The few who remain.
What is the meaning of "la'Mas Yihyu"?
Radak: Their hearts will melt due to their fear.
Malbim: They will need to pay taxes to Yisrael.
