Isaiah 6:6-8

Then flew one of the seraphims unto me, having a live coal in his hand, which he had taken with the tongs from off the altar: And he laid it upon my mouth, and said, Lo, this hath touched thy lips; and thine iniquity is taken away, and thy sin purged. Also I heard the voice of the Lord, saying, Whom shall I send, and who will go for us? Then said I, Here am I; send me.

 

Only after Isaiah had been “cleansed”, did he hear the call of the LORD. He quickly consecrated himself to the Lord and was given his commission.