Then said I, Woe is me! for I am undone; because I am a man of unclean lips, and I dwell in the midst of a people of unclean lips: for mine eyes have seen the King, the LORD of hosts.
It should help us to be concerned about the quality of our worship when we consider that Isaiah’s reaction was a feeling of absolute profaneness in the presence of the moral purity of the divine Being. Consider that Isaiah was a commendable young man—cultured, religious and a cousin of the king. He would have made a good deacon in any church. Today he would be asked to serve on one of our mission boards.
But here Isaiah was an astonished man. He was struck with awe, his whole world suddenly dissolving into a vast, eternal brightness. He was pinned against that brightness—red and black, the colors of sin.
What had happened? Isaiah, only human, had glimpsed One whose character and nature signaled perfection. He could only manage the witness: “Mine eyes have seen the King.” WHT072-073
Lord, how can I help but fall on my face before You if I once get a glimpse of Your great glory? Forgive my sinfulness as I fall before You in worship. Amen. 
5 The word translated “woe” here (ʾôy; GK 208) is different from that used several times in ch. 5 (hôy [GK 2098], vv. 8, 11, 20–22), though they are similar in form and pronunciation and identical in meaning. They are, in fact, synonyms, each possessing various nuances ranging from a threat to a sigh. If this part of the book has been arranged with an eye more to its message than to its chronology, this “woe” may have been viewed as the climax of the series that began at 5:8. The reference in this verse to the people’s sin strengthens this possibility, the more so as sins of the tongue have found their place in ch. 5 at least twice (5:18–20) and possibly a third time, for acquittal (5:23) was made known by a pronouncement of the judge.
This verse teaches us that in order to be an effective channel for God’s penetrating word, the power of that word must be felt in the person’s own conscience. Wildberger (in loc.) says, “This terror is itself an element of the theophany (cf. Ge 32:30; Ex 3:6; Jdg 6:22; 13:22). Those who utter such a cry of woe about themselves are witnessing to the fact that their very existence is threatened” (cf. also Watts, in loc.).
It is true that the lips of the prophet were destined to proclaim God’s truth; but if he was in the temple at worship (see comment on v. 1), the primary reference may be to the defiled lips of the worshiper (cf. 1:15; 29:13). The people of the OT always felt a deep apprehension at the prospect of seeing God (Ge 32:20; Ex 33:20; Jdg 6:22; 13:21–22). This must have been underlined still more for Isaiah as he saw even the unfallen seraphs covering their faces in the presence of the Most High.
6:5 unclean lips. If the lips are unclean, so is the heart. This vision of God’s holiness vividly reminded the prophet of his own unworthiness which deserved judgment. Job (Job 42:6) and Peter (Lk 5:8) came to the same realization about themselves when confronted with the presence of the Lord (cf. Eze 1:28–2:7; Rev 1:17).
6:5 Woe is me. Isaiah is astonished by the glory of God; like Peter he becomes afraid (cf. Luke 5:8). He pronounces an oracular curse upon himself. His conviction of sin is specific: he has unclean lips. The fact that others around him suffer from the same condition compounds his sin rather than alleviating it.
 Tozer, A. W., & Eggert, R. (2015). Tozer on the almighty god: a 365-day devotional. Chicago, IL: Moody Publishers.
 Grogan, G. W. (2008). Isaiah. In T. Longman III, Garland David E. (Eds.), The Expositor’s Bible Commentary: Proverbs–Isaiah (Revised Edition) (Vol. 6, pp. 507–508). Grand Rapids, MI: Zondervan.
 MacArthur, J. F., Jr. (2006). The MacArthur study Bible: New American Standard Bible. (Is 6:5). Nashville, TN: Thomas Nelson Publishers.
 Sproul, R. C. (Ed.). (2015). The Reformation Study Bible: English Standard Version (2015 Edition) (p. 1132). Orlando, FL: Reformation Trust.