So I said: “Woe is me, for I am undone! Because I am a man of unclean lips, and I dwell in the midst of a people of unclean lips; for my eyes have seen the King, the LORD of hosts.”
Then one of the seraphim flew to me, having in his hand a live coal which he had taken with the tongs from the altar. And he touched my mouth with it, and said: “Behold, this has touched your lips; your iniquity is taken away, and your sin purged.”
Also I heard the voice of the Lord, saying: “Whom shall I send, and who will go for Us?”
Then I said, “Here am I! Send me.”
And He said, “Go, and tell this people: ‘Keep on hearing, but do not understand; keep on seeing, but do not perceive.’ Make the heart of this people dull, and their ears heavy, and shut their eyes; lest they see with their eyes, and hear with their ears, and understand with their heart, and return and be healed.”
Isaiah 6:1-10 (NKJV)