He had nowhere to stand. Every last security he possessed evaporated like a water droplet beneath a blow-torch. We'll have to write it up so others can see if it's meaningful for them too. Woe is me. Plainly he is horrified.
Lips express what is hidden in the heart.
Unclean lips mean defiled heart. Because his heart is defiled there's no chance he can make his unclean lips clean, acceptable to God. But every last person in his community is similarly defiled, corrupted, sin-riddled throughout. Then God is the one to make clean what is now filthy and putrid. The horror is as unendurable as the annihilation is inescapable.