God Within The Darkness

(20:18, in some editions 17) ויעמוד העם מרחוק ומשה נגש אל הערפל אשר שם האלקים "The people remained far off, but Moses drew near to the opaque darkness, where God was."

Rebbe Nachman teaches (Likutay Moharan 115) that often when a person has been far from Hashem and then he decides to come close, there will be challenges that stand before.  The evil side says its not fair that he can all of a sudden come close after years of violating and abusing the Torah.  Many people get turned off by the challenge placed before them.  People feel its not right, if Hashem wants me to be close to Him, to improve myself, then it should be easy.  However, Rebbe Nachman says that is a grave mistake, Hashem is in that roadblock, that challenge that is in front of you.  He wants to plow through the block head on and that way you will be able to "find Hashem."  
This is hinted to in this verse, when people see the darkness in front of them they stand back, they are discouraged.  However, one who is smart, has the daas like Moshe moves toward the darkness and attacks it head-on.     
Rabbi Nasan Maimon adds that the numerical value of ערפל is the same as שכינה to allude to this idea that Hashem is hidden within the darkness.