Why does it say "Chazon"?
Rashi: It is harsh rebuke 1 . Chazon is the harshest of 10 expressions of Nevu'ah (Bereishis Rabah 44:7) - "Chazus Kasheh Hugad Li" (21:2).
Radak (2): His generation was evil. Even though it says about Uziyah "va'Ya'as ha'Yashar b'Einei Hashem" (Melachim II, 15:3), and also Yosam, it says about Uziyah "uch'Chezkaso Gavah Libo Ad Lehashchis" (Divrei ha'Yamim II, 26:16). In the days of both of them, people sacrificed on Bamos. In Yosam's days, "Od ha'Am Mashchisim" (Divrei ha'Yamim II, 27:2), and all the more so in the days of Achaz, who did great evils (ibid., 28:2). The entire nation was evil in his days - "b'Azvam Es Hashem Elokei Avosam" (ibid., 6). Also in the days of Chizkiyah, their hearts were not complete with Hashem, like it says in Divrei ha'Yamim.
What do we know about Amotz, Yeshayah's father?
Rashi (from Megilah 10b): We have a tradition that Amotz was the brother of Amatziyah Melech Yehudah. Radak - if not for the tradition, we would not know from what Shevet he was!
Megilah 15a: If a Navi's father's name is mentioned with his son's name, also his father was a Navi. If not, he was not 1 .
Megilah 15a: If his city is mentioned, he was from that city; if not, he was from Yerushalayim.
Why does it say "Al Yehudah vi'Yrushalayim"? He prophesized about many nations - "Masa Bavel", "Masa Mo'av" (13:1, 15:1)!
Rashi (from Mechilta, Shirah 7): This teaches that this is not the beginning of Sefer Yeshayah. This part of the Sefer is about Yehudah and Yerushalayim 1 , just like those are about Bavel and Mo'av. The Sefer begins "bi'Shnas Mos ha'Melech Uziyah" (6:1); the Navi is not [always] in chronological order. We must say so, for on the day of the earthquake, Uziyah became a Metzora, and Hashem said "whom will I send
Malbim: Verses 2-21 are about Yehudah, and 21-27 are about Yerushalayim. The rest of the Perek is about both of them.
Malbim: There are three [other] proofs. (a) Why does it say that he saw about Yehudah and Yerushalayim? The Sefer discusses also the 10 tribes and other nations! Rather, here is a particular vision. (b) If this began the Sefer, it should have said 'Chezyonos' to include all his visions. (c) "Chazon" is a particular level of Nevu'ah. If this began the Sefer, it should have said 'Divrei Yeshayah' to include all kinds of his Nevu'ah, e.g. Masa, like it says "Divrei Yirmeyah" (Yirmeyah 1:1).
Why does it mention these four kings?
Rashi: He prophesized in all the days of these kings. Shechinah came on him on the day that Uziyah became a Metzora (refer to 1:1:3:1), and he prophesized until Menasheh killed him.
Malbim: He had this Nevu'ah in the days of Uziyah, and repeated it in the days of each of these kings.
