Why does it say "ba'Yom ha'Hu Yegalach Hashem... b'Melech Ashur"?
Sanhedrin 95b, cited in Rashi: Hashem assumed the guise of an old man, and came (Ramah - Hashem prompted an old man to come) in front of Sancheriv He suggested to shave him to disguise him; lest kings of the east and west confront him [for taking their princes to witness his expected victory, and they all died]
Radak: This refers to the plague in Machaneh Ashur after it conquered the rest of Eretz Yisrael and came to Yerushalayim. An angel struck the camp (Melachim II, 19:35) . The plague is compared to a razor, for it totally eradicates the hair. So the plague was great among them and their Gedolim - "va'Yichached Kol Gibor Chayil v'Nagid v'Sar b,Machaneh Melech Ashur" (Divrei ha'Yamim II, 32:21).
Malbim: This is in the days of Achaz. Hashem will use Melech Ashur to shave (destroy Damesek and Shomron).
What is "[b'Sa'ar] ha'Sechirah"?
Sanhedrin 95b: Sancheriv wanted to shave (refer to 7:20:1:1).He needed to grind pits in order to rent a razor.
Rashi: "Ha'Sechirah" is big; Targum Yonasan of "Gam Sechireha" (Yirmeyah 46:21) is 'Af Ravrivaha.'
Radak: A rented razor is good and sharp.
Malbim: The verse depicts Melech Ashur as a razor used to remove hair.
What is "[ha'Sechirah] b'Evrei Nahar"?
Sanhedrin 95b: Sancheriv needed to grind pits (refer to 7:20:2:1) - this is work normally done by the river.
Rashi: Among people who live on the other side of the river. Whom is this? Melech Ashur 1 .
Radak: This is an army that came from the other side of the river, i.e. Sancheriv and his troops who came to Yerushalayim.
Also Malbim explains so, just he holds that Melech Ashur is the razor, and not the one who is shaved. (PF)
What are the "Rosh", "Raglayim" and "Zakan"?
Rashi: These refer to Sancheriv, his camp and his rulers, respectively.
Radak: "Rosh" refers to hair of the head - "v'Gilach Es Rosho" (Bamidbar 6:9). This is a metaphor for the heads of his troops. "Raglayim" refers to hair of the Ervah, i.e. the commoners. "Zakan" refers to the king.
Malbim: It was normal to shave all hair of the head. Kohanim may not serve if their hair is long (30 days growth), and a king cuts his hair every day. Also hair of the legs is repulsive, but it is not exposed. The razor (Melech Ashur) will shave the head (great, known Resha'im) and the legs (covert sinners). Also refer to 7:20:5:4.
What is the meaning of "["v'Gam Es ha'Zakan] Tispeh"?
Sanhedrin 95b, cited in Rashi: Sancheriv was blowing a fire to enable a to cut his hair at night (refer to 7:20:1:1). His beard caught fire, and it consumed all the hair of his beard and face 1 .
Rashi: It will be finished. Shaving is [a metaphor for] killing; the razor is the sword.
Radak: It says "v'Gam [Es ha'Zakan]" because it is not normal to shave the beard with a razor. Even one who shaves his head does not shave the beard; people do shave hair of the Ervah . It says "Tispeh", and not Yegale'ach, for Melech Ashur did not die in the camp, rather, in his land, when he returned. His sons struck him with the sword (Melachim II, 19:37). Tispeh is Po'el Omed (the action applies only to the subject). It applies to Zakan, which is sometimes feminine - "v'Chol 'Zakan Geru'ah" (Yirmeyah 48:37).
Malbim: Once the destroyer has permission, he does not distinguish between good and evil (Bava Kama 60a). The razor itself (not via Hashem) will remove also the beard (Tzadikim), which is grown for honor and beauty. Cutting it is not Gilu'ach, rather, destruction.
Maharal (95b): Hashem 'shaved' Sancheriv of all his grandeur. He used to be a world ruler, and now he had no soldiers left. He feared the other kings (whom he used to exile to different places) so much that he had to disguise himself.)
