Part 2: Confession (verse 5)
The holiness with which Isaiah was confronted was the holiness that had destroyed Nadab and Abihu (the sons of Aaron) when the Tabernacle was first set up. No wonder he was terrified. The vision gave him no pleasure; for when we see God as He really is, we see ourselves as we really are. And Isaiah became horribly aware that he was a sinful human being who had no right to be even on the very fringe of God’s presence.
In the presence of absolute holiness, degrees of sinfulness become irrelevant. Isaiah could not consider himself to be any better than the rest of his people – the people who should have been holy to God, but were anything but! And we are no better…
Why does he mention his lips, specifically? Perhaps because he was already acting as a prophet, and now realises how unworthy he is of such a calling. But since he describes the whole nation in the same way (“I live among a people of unclean lips”), he is probably referring to the very close relationship between the heart and the tongue. “How can you who are evil say anything good? For the mouth speaks what the heart is full of.” (Matthew 12:34)