“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.’ Then 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: 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.’ Also 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.’” Isaiah 6:5-8 (KJV)

When the LORD had revealed Himself to the prophet he was weak in the knees, and fell before the Almighty, realizing he was undone and unclean. 

When we meet God, through His Son Jesus Christ (which is the only way to meet God), we realize our uncleanness, our undoneness, our unholiness, and we fall on His grace, and into His grace.

The fire [live coal] of the Spirit and the Word do a work of cleansing in us, and we are made clean and made right for the presence of Holy God.

Our response to being cleansed by God is to hear His word and we realize there are people who do not know Him.  We hear God’s call and like Isaiah we will say, “Here am I; send me”.

Trust in the work of Jesus on the cross for you.  Call on His name believing Him.