Why does it say "l'Marbe ha'Mishrah"?
Rashi #1: Whom will Hashem call so ("Sar Shalom" - 5)? To the king who will increase Hashem's authority over himself, to fear Him. Mishrah is an expression of authority. 1
Rashi #2: The son is given great kingship.
Malbim: Normally, if there is great authority, there cannot be great Shalom, for envy is arpused. Here, both will coincide.
Why is the Mem in "l'Marbe" closed (like a final Mem)?
Sanhedrin 94a: Hashem wanted to make Chizkiyah Mashi'ach 1 , and Sancheriv (would have fulfilled the prophecy of) Gog and Magog. Midas ha'Din protested David sang so many praises to You, but You did not make him Mashi'ach. You did great miracles for Chizkiyah, and he did not sing Shirah 2 . Will You make him Mashi'ach?! (The closed Mem represents the closure of Hashem's intention, or that Hashem wanted to cease Yisrael's affliction, or that because Chizkiyah's mouth was closed, it did not happen.)
Radak: In Nechemyah (2;13), The final Mem is "Perutzim" is open like a regular Mem. When the walls of Yerushalayim will be sealed - during the entire Galus, they are Perutzim (breached), and at the time of the salvation, they will be sealed - then will be opened the Mishrah (authority), which is sealed until Melech ha'Mashi'ach.
Teshuvas ha'Ravaz (YD 37): It hints to a ring for Kidushin. Initially he could not be Mashi'ach, who will not come until all Neshamos in Guf come to the world (Yevamos 62a), for he did not engage in Peru u'Rvu. After he married, this verse was said; he could have been Mashi'ach (refer to 9:6:2:1). The Gematriya of l'Marbe is the same as Ezer or Zera (which hint to marriage and children).
Yevamos 62a: Ben David will not come until all Neshamos in Guf (Rashi 62a - a storehouse) are finished (came to the world). If so, how could Chizkiyah have become Mashi'ach? Tosfos Nidah 13a DH Ad - women would have given birth to many at once, in order that all the Neshamos be born first. Alshich (Michah 5) - Guf is not a storehouse. Rather, it is the body of Adam ha'Rishon. These Neshamos were in Ko'ach Adam. This is only if the ruler will be Ben David, for his origin was in Adam ha'Rishon (Bereishis Rabasi 26 - Hashem gave to Adam ha'Rishon one day, i.e. 1000 years; he left 70 for David). Therefore, he must fix the Neshamos that he ruined. Chizkiyah is not Adam, so this does not apply (he could be Mashi'ach before all Neshamos are born. I do not understand. Also Chizkiyah is from David! - PF).
An addition in Rashi: Because Chizkiyah cut off the doors of the Heichal and sent them to Melech Ashur, he was not made Mashi'ach.
Why does it say "ul'Shalom Ein Ketz"?
Rashi: There is no end to the Shalom; he will have peace on all sides. "Ketz" is not a limit in time, rather, borders around. Because Chizkiyah increased Hashem's authority over himself (refer to 9:6:1:1), his reward is unlimited Shalom.
Why does it say "Al Kisei David" and also "v'Al Mamlachto"?
Radak: The matter is repeated in different words.
Malbim: "Al Kisei David" corresponds to "l'Marbe ha'Mishrah"; he will have great authority. "V'Al Mamlachto" corresponds to ul'Shalom" - his kingdom and country will have great Shalom - "v'Cherev Lo Sa'avor b'Artzechem" (Vayikra 26:6).
What is the meaning of "ul'Sa'adah"?
Rashi: His kingship and authority will never falter. Even though there will be an interruption during the Galus, it will return to its previous state.
Why does it say "b'Mishpat uvi'Tzdakah"?
Rashi: This Shalom will be on Kisei Malchus David, with Mishpat and Tzedakah that Chizkiyah did.
Radak: They will found his throne and cause his kingship to last.
Malbim: Mishpat will prepare his throne me'Atah. A king is appointed to do justice Bein Adam l'Chavero! If not for fear of the king, a man would swallow his colleague (Avos 3:2). Tzedakah (proper deeds Bein Adam la'Makom) will make it last v'Ad Olam - "v'Chasav Lo Es Mishnah ha'Torah?; v'Haysah Imo?; Lema'an Ya'arich Yamim Al Mamlachto" (Devarim 17:18-20).
What is "me'Atah v'Ad Olam"?
Rashi: To the Olam (world) of Chizkiyah, i.e. all his days 1 . So Chanah said about Shmuel "v'Yashav Sham Ad Olam" (Shmuel I, 1:22).
Malbim: Refer to 9:6:6:3.
Rashi: From here we can refute heretics who attribute divinity to their false Mashi'ach. It says "from now", and their savior was born [more than] 300 years later!
What is "Kin'as Hashem Tzevakos"?
Rashi: He was zealous for Tziyon, because Aram and Pekach counseled about [conquering] it.
Radak: It is Hashem's anger at the words of Melech Ashur's youths, who blasphemed Hashem.
Why does it say "Ta'aseh Zos"?
Rashi: Achaz is not worthy of this, and merit of the Avos finished.
Malbim: Yisrael are not worthy of this; Hashem will do so due to [Kin'ah for] His great name.
