Hmmmm, sounds like a 'stress' dream to me. Other than considering what might have triggered that I personally would not be worrying about the subject matter as, quite frankly, the Devil does not exist. That doesn't take away from the frightening and disturbing tone however. But, if you concentrate more on telling yourself such a thing doesn't exist the easier it is going to be recovering from this dream. Questioning it and spending time thinking about the meaning of the appearance of the apparition is only going to make it all feel more disturbing and the worse. You are better off not ruminating about the subject. Of course, this is only my opinion.