Staring at their radiance, I'm reminded of Isaiah's encounter with God:
"I am doomed," he said, "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.” 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” (Is. 6:5-7).Consider for a moment: the coal was so hot a celestial being (a seraphim) had to hold it with tongs. Yet that same burning coal touched Isaiah's soft, thin lips. I burn my mouth on a piece of hot toast and tears well up in my eyes!
True, this was a vision, probably not an actual event. Nevertheless, I've had dreams that were so real, I awakened believing those events actually occurred. I bet it was similar for Isaiah. I suspect there was a sting to his lips when the vision was over. A reminder of the pain, the cost of reconciliation and atonement. The burning sensation's effect was so much greater than simply washing his mouth out with soap.
Human lips have about 5 layers of skin as opposed to the 16 or so layers covering the rest of the face. That's why they're typically darker; the blood is so much closer to the surface. I think it's poignant God cleanses Isaiah's (acknowledged) unclean lips. Sin that's close to the surface of our hearts and minds is more easily "cleaned-up" than those things we bury deep within. Isaiah's confession was at the ready; I hope I'm that attentive to keeping accounts with God short, so he can do his cleansing work. No matter how much it hurts. For it's then he can most effectively "send me” (Is. 6:8).