The pivots on the thresholds shook at the voices of those who called, and the house filled with smoke. And I said: ‘Woe is me! I am lost, for I am a man of unclean lips, and I live among a people of unclean lips; yet my eyes have seen the King, the LORD of hosts!’
Then one of the seraphs flew to me, holding a live coal that had been taken from the altar with a pair of tongs. The seraph touched my mouth with it and said: ‘Now that this has touched your lips, your guilt has departed and your sin is blotted out.’ Then I heard the voice of the Lord saying, ‘Whom shall I send, and who will go for us?’ And I said, ‘Here am I; send me!’" (Isaiah 6:1-8)
King Uzziah was, by most standards, one of the best kings of Judah - and certainly better than the ones in the kingdom of Israel, next door. He was no Prince Charles - took the throne at the age of 16, ruled a very long time. He beat up the Philistines, refortified Jerusalem - was generally a success. But he had a flaw.
Uzziah went into the temple and tried to burn incense himself there. Now, the king - however important he thought he was - wasn't allowed to burn incense in the temple. That was the priests' job. The king's job - anointed as he was - was to protect the kingdom, and let it prosper. The priests' job was to run the Temple.
According to the books of Chronicles, Uzziah got his comeuppance for his cheek. He was inflicted with leprosy for the rest of his life, and when he died, because of his leprosy, he was buried separately from the other kings of Judah - so as not to contaminate them with his uncleanness.
And that's why I think it's important that Isaiah gets his vision "in the year that King Uzziah died". The king had tried to raise himself up too high - had challenged the rules of God - and had paid. And the year a king dies is a bit, for the state of Judah, like an election year. Before a General Election, if the result looks close, the Stock Market falls. Afterwards, as the Government is formed, we wonder whether they're actually going to do the things they said. Or, if it's a new party in power, will they promptly stick up taxes, saying they hadn't realised how bad things were? So in Judah - as the king declines - will he succumb to insanity? Will his weakness cause a wave of assassinations of those who might want to push on the process? Will one of his sons stage a coup? When he dies - who is the new king? What are his policies? Will he align with Aram, with Assyria, with Egypt? The state is uncertain. But Isaiah gets to see - not the majesty of a king who ruled all the way to Egypt - but the glory of the King of Kings. The passing glory of the tainted king is contrasted with the eternal glory of the Lord.
There's no uncertainty here. When he sees the Lord in the temple, Isaiah knows exactly who it is. And he cries out something that - in our world where we sometimes see God as cuddly, as endlessly indulgent to us, may seem a bit extreme. But it's something that, if you've just seen the King of Kings, so great that just the hem of his robe fills the temple with glory, and you've seen terrifying angel after terrifying angel surrounding him, makes perfect sense:
‘Woe is me! I am lost, for I am a man of unclean lips, and I live among a people of unclean lips; yet my eyes have seen the King, the LORD of hosts"