“Isaiah was a man of integrity, yet one glimpse of God’s holiness makes him come apart at the seams. As long as our gaze is fixed on the horizontal plane of this earth, we have no problem with ourselves. But if we lift our gaze to heaven and contemplate what God is, we will be broken. Security and smugness is annihilated. Holy men are reduced to trembling with one glimpse of God.

When Isaiah discovers who God is he pronounces an oracle of doom on himself—a curse. The first time he saw what God is was the first time he saw who he was. He saw that he had a dirty mouth and that his dirtiness was epidemic, pandemic.”

from www.desiringgod.org