Isaiah 6

As Isaiah saw the Lord and was called on a "mission", we receive some sound counsel for all that are called into the service of the Lord.  Isaiah, having seen the Lord, His throne and habitation declares -

"...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."  (Old Testament | Isaiah 6:5)

Being overwhelmed (undone), I see the words "unclean lips" to represent  a feeling of being unqualified to speak the words of the Lord, more than one that is imperfect...which would also apply.  Under these conditions -

"...flew one of the seraphims unto me, having a live coal in his hand, which he had taken with the tongs from off the altar:
7 And he laid it upon my mouth, and said, Lo, this hath touched thy lips; and thine iniquity is taken away, and thy sin purged."  (Old Testament | Isaiah 6:6 - 7)

It is through the atonement of Jesus Christ and the power of the Holy Ghost we are made clean and  qualified for the Savior said-

"Yea, blessed are they who shall believe in your words, and come down into the depths of humility and be baptized, for they shall be visited with fire and with the Holy Ghost, and shall receive a remission of their sins."  (Book of Mormon | 3 Nephi 12:2)

The live coal on his lips was symbolic of this process for Isaiah.  And it was then, having faith in the atonement that Isaiah says -

"...I heard the voice of the Lord, saying, Whom shall I send, and who will go for us? Then said I, Here am I; send me."  (Old Testament | Isaiah 6:8)

And thus Isaiah accepted the call in the work of salvation.  As he does he is counseled -

"...Go, and tell this people, Hear ye indeed, but [they] understand not; and see ye indeed, but [they]perceive not.
10 Make the heart of this people fat, and make their ears heavy, and shut their eyes; lest they see with their eyes, and hear with their ears, and understand with their heart, and convert, and be healed.
11 Then said I, Lord, how long? And he answered, Until the cities be wasted without inhabitant, and the houses without man, and the land be utterly desolate..."  (Old Testament | Isaiah 6:9 - 11)

I added "they" to match the writings in 2nd Nephi.  To help Isaiah understand what he is up against in his mission, I believe it would have been more understandable in our day had Isaiah could have used "Imagine in your mind" in lieu of "make" suggesting this is what you are up against.  And obviously, "how long?"...This work will continue until the end.

I love the promise after utter desolation -

"But yet in it shall be a tenth, and it shall return..."  (Old Testament | Isaiah 6:13)

This may have reference to return of Judah from Babylon, but I wonder if it symbolic of those that will qualify for exaltation.