The book of Isaiah covers a huge amount of time and history of the kingdom of Judah. It places a strong emphasis on the holiness of God. Holiness acquired a moral significance that it had not had before. God’s holiness was understood to be his perfect moral purity, in combination with his transcendent exaltation.
The new insight into the meaning of holiness brought new insight also into the meaning of sin and judgment. No prophet spoke out more fearlessly than Isaiah against the pride of Judah, her selfish indulgence and her callous injustice toward the poor.
Another important teaching is the belief that God was directing all history in accordance with his purpose of establishing his rule on earth. In chapter 10 which belongs to the time of the invasion of Palestine in 701 B.C., when the Assyrians had reached the zenith of their power and seemed to be invincible, Isaiah came to see that a pagan nation could be used to chastise the people of God.
History and doctrine are closely intertwined in the book of Isaiah. Jesus as Messiah is anticipated particularly in Chapter 52:13-53:12.