Prophet Isaiah describes God's judgement and restoration of Judah and Jerusalem before and after the Exile of the Israelites to Babylon.
The book describes how God will make Jerusalem the center of his worldwide rule through a saviour or messiah who will destroy the oppressor (Babylon). This messiah is the Persian king Cyrus the Great, who is an agent of God to this end. Isaiah speaks against corrupt leaders while supporting the disadvantaged, and places righteousness in God's holiness rather than in Israel's covenant.
Isaiah contains many important developments in the Bible. 44:6 contains the first clear statement of monotheism: "I am the first, and I am the last; and beside me there is no God." Isaiah 2:4 contains an enduring statement on peace after war: "And he shall judge among the nations, and shall rebuke many people: and they shall beat their swords into plowshares, and their spears into pruninghooks: nation shall not lift up sword against nation, neither shall they learn war any more." And Christians see 40:3 which says, "The voice of him that crieth in the wilderness, Prepare ye the way of the LORD, make straight in the desert a highway for our God." as foreshadowing John the Baptist's later preaching about the coming of Christ.