Once people confronts the holiness of God, they sees themselves! Put another way, it is difficult for a person to see how much they need God without first knowing how holy he is and how corrupt they are. That is what happened to Isaiah, God’s holiness revealed his wretchedness, vileness and unworthiness before him.
The only conclusion possible after realizing such hopelessness was to cry out, “Woe is me! for I am undone; because I am a man of unclean lips”. This powerful word spoken by the prophet, not only emphasize his sinfulness, but his fear of seeing “...the King, the LORD of hosts” (Isaiah 6:5). Surely, in his mind, death was imminent!
The prophet gives two reasons for such a damning conclusion. First, he is a “man with unclean lips”. He stresses unclean lips and not heart because the lips express the desire and thoughts of the heart (Romans 10:9). Isaiah knew that, unlike the beings surrounding the LORD’s throne, his lips did not continuously sing the praises of God, not necessarily because he did not want to, but his evil heart would never allow it (Romans 7:21,23).
Second, he pronounces on himself the only sentence appropriate for his situation--woe! Once a person comes face‑to‑face with God, they see their own sinfulness and their utter defilement. He suddenly realized that not only were his lips unclean but his countrymen were in the same predicament. Their lips to, did not pour forth praises to God as they should have.
This is behind Isaiah’s proclamation, “for I am undone”, which literally means ruined’ or ‘perish’. For him, there was no future or hope! Most would have begged God for compassion and mercy at this point, or made some incredible oath if given another chance. However, Isaiah did none of these, the text seems to imply a willingness on his part to take whatever judgment God had for him.