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. – Isaiah 6:6,7

Then came the best part of the vision for Isaiah. At the glorious sight, he felt, “Woe is me, for I am undone, I am stricken dumb. I can never speak again, for my lips are unclean, and I dwell among an unclean people.” Then, swift as lightning flew a seraph, bringing a coal more burning than himself from off the altar of sacrifice, wherewith he touched the prophet’s lip. Beloved, this is what we need. We need to feel the atonement laid home to us, to feel the power of the great sacrifice of Christ, to hear a voice saying within our spirit, “Thine iniquity is put away, and thy sin is purged.” Though that live coal must have blistered the lip which it covered, yet it made it eloquent. Common fire would destroy the organs of speech, but the fire of sacrifice does not so, but it unlooses a grateful tongue, and helps a grateful heart to tell the love immense, unsearchable, which offered itself upon the altar of sacrifice, that holiness and love might save the sinner. Our peace comes from the Holy, Holy, Holy One, who is just, and yet forgives His people’s sin. Brother, if you are to proclaim the glory of your Lord, you must feel the sacrificial coal applied to the place where your impurity is most seen, even to your lips; you must know that you are forgiven; for your conviction that you are clean before God will give you confidence in telling out to others the story of the cross.~ C.H. Spurgeon

https://www.blueletterbible.org/Comm/spurgeon_charles/sermons/1844.cfm