Isaiah 6

"Then I said, 'It’s all over! I am doomed, for I am a sinful man. I have filthy lips, and I live among a people with filthy lips. Yet I have seen the King, the Lord of Heaven’s Armies.'
Then one of the seraphim flew to me with a burning coal he had taken from the altar with a pair of tongs. He touched my lips with it and said, 'See, this coal has touched your lips. Now your guilt is removed, and your sins are forgiven.'
Then I heard the Lord asking, 'Whom should I send as a messenger to this people? Who will go for us?'
I said, 'Here I am. Send me.'" v. 5-8
Seeing the Lord and listening to the praise of the angles, Isaiah realized that he was sinful before God, with no hope of measuring up to God standard of holiness. When Isaiah's lips were touched with a live burning coal, however, he was told that his sins were forgiven. It wasn't the coal that cleansed him, but God. In response, Isaiah submitted himself entirely to God's service. No matter how dificult his task would be, he said, "Here I am. Send me." The painful cleansing process was necessary before Isaiah could fulfill the task to which God was calling him. Before we accept God's call to speak for him to those around us we must be cleansed as Isaiah was, confessing our sins and submitting to God's control. Letting God purify us may be painful, but we must be purified so that we can truly represent God, who is pure and holy.

Taken from the NLT Life Application Study Bible