What happens when Harry realizes he could kill everyone in the house right then?

Harry thinks about the fact that he could call down fire and destroy the house and everyone in it. Harry knows that he could do this and not have to face Victor Sells and that Victor Sells deserves to die. Harry is beginning to be consumed by his hate when he suddenly feels the weight from his mother's talisman. Harry has to remind himself that he isn't a murderer and that he is a wizard who draws from life and tries to preserve it, not destroy it.