Sefer Yeshayahu (Isaiah) is the book of the prophecies of Yeshayahu ben Amotz, one of the books of the Neviim Acharonim (the Later Prophets). Yeshayahu speaks to Yehudah (Judah) and Yerushalayim (Jerusalem) in the days of four kings of Yehudah, Uziyahu (Uzziah), Yotam, Achaz and Chizkiyahu (Hezekiah), son of Achaz (1:1).
The book opens with a rebuke of Yehudah, whose korbanot (offerings to Hashem) Hashem does not want while their hands are full of injustice, and with a vision of the end of days, when the nations will stream to the mountain of Hashem. In the year King Uziyahu dies, Yeshayahu sees Hashem on a high throne, with serafim (fiery angels) calling "Kadosh, kadosh, kadosh" (holy, holy, holy), and he accepts Hashem's mission to the people. (These words are said in Kedushah in the repetition of the Amidah.) He tells King Achaz not to fear Aram and Yisrael. He foretells the fall of Ashur (Assyria) and a king from the shoot of Yishai (Jesse) who will judge with justice (Chazal understand this king as the Mashiach).
Then come prophecies against the nations, each a massa (prophecy concerning), among them Bavel (Babylon), Ashur, Moav, Damesek (Damascus), Mitzrayim (Egypt) and Tzor (Tyre), followed by a judgment of the whole earth and songs of deliverance. Yeshayahu warns Efrayim (the northern kingdom) and Yerushalayim against trusting Mitzrayim instead of Hashem.
Perakim 36–39 tell how Hashem saves Yerushalayim from Sancheriv (Sennacherib) king of Ashur, how Chizkiyahu is healed of his illness, and how he shows his treasures to envoys from Bavel. (The same events are told in Melachim Bet, perakim 18–20.)
From perek 40 the book turns to comfort. Hashem promises that the exiles will return from Bavel, and He names Koresh (Cyrus) as the king who will order Yerushalayim rebuilt. Hashem alone created all and rules all, and the idols are nothing. Yaakov, Bnei Yisrael (the children of Israel), is His servant (Rashi explains that the servant of perek 53, who suffers and is then raised up, is the people of Israel spoken of as one man). Tziyon (Zion) will be rebuilt and filled with her children. Hashem asks for a fast of kindness to the poor (58), promises that the nations will come to the light of Yerushalayim (60), and closes with a new heaven and earth, where all flesh comes to bow before Him (65–66).
Sefer Yeshayahu has sixty-six perakim, and many haftarot come from it. They include all seven haftarot of consolation after Tisha B'Av, from Parshat Vaetchanan through Nitzavim, Shabbat Chazon (Parshat Devarim), the haftarot of Parshat Bereishit, Noach, Lech Lecha, Shemot, Yitro and Vayikra, and the haftarot of Yom Kippur morning, Mincha on fast days, the eighth day of Pesach (outside Israel) and Shabbat Rosh Chodesh.