Rev 7:9-15

John had a vision of heaven in which he saw a multitude of people from every nation and tongue. These people came out of great tribulation and they have washed their robes in the Blood of the Lamb and made them white as snow.

A certain elderly lady visited KSB. She had been a Christian from her youth, but it was a mystery to her how they washed their robes in the Blood of the Lamb and made them white as snow. However, God revealed the mystery to her and she confessed her sins and cleansed her life.

If we hide our sin we shall not prosper, but if we confess and forsake it we shall obtain pardon. 

Isaiah was a great preacher. In the beginning of the book of Isaiah we read how he pleads with the nation to reconcile themselves with God. But in chapter 6 when he meets with God, he cries out "woe to me, for I am undone! I am a man of unclean lips and dwell among a people of unclean lips". He cried like a lost person when he met God in His holiness.
When it's dark we cannot see dirt; but in the light it is revealed.