The Vision of the King

Isaiah begins with the observation that this is what he saw concerning Judah and Jerusalem in the days of Uzziah, Jotham, Ahaz, and Hezekiah (1:1). But in the 6th chapter, the Lord gave Isaiah a vision of the true King, the exalted Jesus, high and lifted up (John 12:41).
The vision was to prepare Isaiah for his work pronouncing judgment upon the apostate nation. To do so, Isaiah must be shown the depth of his own sin and depravity.
In this glorious scene of the heavenly throne, Isaiah is rightly terrified and convinced that he is about to die. Christ is holy, he is not. Faced with this reality, the prophet confesses his sin and receives cleansing and pardon. Grace is often disguised in the garments of judgment.