How Do You Know?

 How do you know when God is speaking directly to you?  Have you ever experienced it?   

The reason I ask is that I was reading Job 4 this morning.  Job's friend Eliphaz had a dream or a vision.  Here, let him describe it.   
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Job 4:12-17  12 “Now a word was secretly brought to me, 
And my ear received a whisper of it. 
13 In disquieting thoughts from the visions of the night, 
When deep sleep falls on men, 
14 Fear came upon me, and trembling, 
Which made all my bones shake. 
15 Then a spirit passed before my face; 
The hair on my body stood up. 
16 It stood still, 
But I could not discern its appearance. 
A form was before my eyes; 
There was silence; 
Then I heard a voice saying: 
17 ‘Can a mortal be more righteous than God? 
Can a man be more pure than his Maker?  

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That passage could be interpreted a couple of ways.   
 
Some might say it was God speaking to him in his dream.  Others such as myself might see that as Satan whispering in his ear, casting doubt and descension.     
 
Here are two things from this passage that make me think it was Satan.   
 
Eliphaz describes it as an undiscernible form.  I look to the story of Moses for this answer.  When God spoke to Moses on the mountain God covered his face so Moses couldn't see it but God did have shape and form and Moses had no question that is was God speaking to him. 
 
Secondly I would say the same exact thing.  When God has spoken to me there has never been any doubt that it was God.   
 
Make sense?