‘Then Hezekiah said to Isaiah, “The word of Yahweh which you have spoken is good.” He said moreover, “For there will be peace and truth in my days.” '
That Hezekiah lacked Messianic ambition comes out clearly here. He was not concerned with the distant future. He had no vision of the future that God had promised through Isaiah. He was simply satisfied that it meant that in his own day peace and truth would prevail. He was quite prepared for the future house of David to be in slavery (what a contrast with Psalms 2) as long as he could have freedom now. How totally different he was from the coming Servant. No wonder the coming King would have to be miraculously born. David's sons were to become eunuchs because of his folly! The words confirmed the promise that God had made of deliverance from Assyria and beyond that Hezekiah was not concerned. But it was the deathknell of any hopes of a Deliverer from his house. Israel would have to look elsewhere.
In their division of the book commentators often treat chapter 40 that follows as a new book. But in the Hebrew text Isaiah 40:1 simply continues on from Isaiah 39:8. Furthermore, while there is certainly a massive change of subject, what follows is actually Isaiah's response to this situation. Isaiah 39:8 is a comment indicating that Hezekiah is satisfied with the status quo, and an indicator that he is not fitted to fulfil the role of Israel's Saviour. Chapter 40 onwards indicates that Yahweh is not satisfied with such a situation because of Who He is (chapter 40), and will Himself find a Saviour (chapter 41-55), Who will save through suffering.