Kyle Newcomer summarizes the book of Isaiah:
Since God’s people had “forsaken the Lord” (Isaiah 1:4) to worship false gods, they “had become as spiritually lifeless as their idols,” and so they must face the coming “day” of the Lord’s judgment, that is, the Babylonian exile. After the exile, their spiritual hardness persists, but God has not abandoned Israel or the nations. He holds out out the hope of a coming day of salvation, a New Exodus, led by the promised Servant-King, who would save through pouring out his soul to death, and bearing the sins of his people (Isaiah 53:12).
And here’s its shorter version:
The Lord’s day of judgment and salvation is coming, and when it does, his glory will be revealed through his anointed Servant-King.