The book of Isaiah is a collection of his prophecies and messages given over many years. Isaiah preached against social injustice and hypocritical religion, but also gave the most comprehensive and greatest number of messianic prophecies, and the clearest revelation of the gospel, in the Old Testament. Isaiah is also the Old Testament prophet most often quoted by the Apostles. In fact, the book of Isaiah is often called "the gospel according to Isaiah" or "the fifth gospel". As such, the book of Isaiah should be studied by every Christian.

Chapters 1-12 focus on judgment and hope for Jerusalem, chapters 13-27 focus on judgment and hope for the nations, chapters 28-39 prophesy of the coming judgment of Jerusalem, chapters 40-48 speak of hope after the exile, chapters 49-55 speak of "the suffering servant" (the messiah), and chapters 56-66 speak of the millennial kingdom. The last section is where we will find the most end-times prophecies, but these prophecies are also interwoven throughout the book of Isaiah.

The name Isaiah means "salvation of Yahweh", and Isaiah's overall message is of both judgment and salvation. God is holy, and cannot allow sin to go unpunished, but He is also merciful and full of grace and compassion. Isaiah preached to a chosen people whose hearts had turned away from God. His message of judgment, along with a hope of salvation, may be more relevant to Christians today, than to anyone at any time in history.