Why does it say "Yivaled Lanu"?
Rashi: Even though Achaz was a Rasha, his son born several years ago to be king after him, will be a Tzadik who serves Hashem.
Radak: The plague in Machaneh Ashur will be in the days of the son (Chizkiyah); it is as if it is in his merit.
Malbim: The salvation will be due to a new occurrence and Mazal.
Why does it add "Ben Nitan Lanu"?
Radak: The matter is repeated in different words.
Malbim: The son will inherit the kingship.
Why does it say "va'Tehi ha'Mishrah Al Shichmo"?
Rashi: Hashem's yoke will be on him; he will engage in Torah and guard Mitzvos and lean his shoulder to [carry] Hashem's load.
Radak: Shichmo always refers to a burden, like "va'Yet Shichmo Lisbol" (Bereishis 49:15), "v'Es Mateh Shichmo" (above, 3), "Yasur Sivlo me'Al Shichmecha" (10:27). Why is it said here about Mishrah (authority)? It is because Achaz served Melech Ashur; he bore [his yoke] on his shoulder. The verse teaches that the child will not have service on his shoulder, rather, authority.
What will be his name, and what is its significance?
Sanhedrin 94a: He has eight names - Pele Yo'etz El Gibor Avi Ad Sar Shalom. Chizkiyah was not his true name. He is called so because Chizko Kah (Hashem strengthened him), or because Chizek (he strengthened) Yisrael to serve Hashem.
Rashi: Hashem, who is Pele Yo'etz (wondrous counsel), Kel Gibor and Avi Ad, will call him Sar Shalom, for there will be Shalom and Emes in his days.
Rashi (6): "Pele Yo'etz? Sar Shalom" are all names of Hashem. The verse does not discuss the son's name. Rather, "va'Yikra Shmo" is for grandeur and authority, like "u'Kra Shem b'Veis Lechem" (Rus 4:11), "v'Asisi Lecha Shem" (Shmuel II, 7:9). Refer to 9:6:1:2.
Radak: Hashem, (i.e. Pele Yo'etz?), will call him Sar Shalom, to hint that he will have authority, and not serve another king - "va'Yamred b'Melech Ashur v'Lo Avado" (Melachim II, 18:7). The names for Hashem teach about Chizkiyah. Pele - due to the wonder [done for him]. The sun went backwards (Melachim II, 20:11). Yo'etz - Hashem's counsel was fulfilled for him, and Sancheriv's counsel was annulled. Kel Gibor - [Hashem] overcame a Gibor [in Chizkiyah's days]. Even though Sancheriv came against him with a great army and Giborim, He overcame them, and in a moment, He struck his camp.Avi Ad - Hashem exists forever, and He is the father of time, and He created it. He has the ability to add or detract, and to add 15 years to Chizkiyah's life.
Malbim: Hashem, (i.e. Pele Yo'etz?), will call him Sar Shalom, to hint that his authority will not be via war, rather, via Shalom. The three descriptions of Hashem show that His promise will be fulfilled without change. There are three reasons why man's promises change. (a) His intent and desire change. This does not apply to Hashem, who is Pele Yo'etz - His counsel does not change. (b) Man's ability is limited; he cannot always fulfill his promise. Hashem is Kel Gibor - He has absolute ability. (c) Man dies, and then his promise 'dies'. Hashem is Avi Ad - the father of eternity who lasts forever.
