Obsidian is a great protective and cleansing stone that will bestow valuable knowledge about your deepest self when you engage with this crystal with conscious intention.
 
Obsidian is best used as a teacher, to show us where our fears lie and how to use the proper mechanics of energy to protect ourselves.  
 
Not through sealing our auras against negativity, but through illuminating it.
 
Obsidian teaches that any attempt to "block negative energies" is neither valuable or even possible, and in fact is simply an attempt to separate based on fear.
 
Obsidian teaches that protection is often a matter of pure focus.  When you are present and aware of circumstances and energy, there is very little chance that you are going to run into trouble.  
 
Obsidian helps us to ground and be present so that our inner warrior can take appropriate action while problems are still small.