I would say that npd is a symptom, a coping mechanism. From my understanding so far, it's a symptom that can manifest itself naturally when the underlying belief of what god is, is a seperate, unconnected being from satan, oneself and from everything else. Or to put it another way, when one thinks of himself as an unconnected entity to anything else. That seperation plants a seed of thinking oneself is something seperate and therefore can be compared.
To study the traits of people is a monumental undertaking when going from ground up. I've found it easier to go from top down - top being the notion of god or no god and if god, then who or what god is and then... practices preached by the various religions and the effects of those on the people.
Jw's are a christian organization who believe that god is a seperate physical entity to self, jesus, satan, holy spirit, creatures and to everything else, driving the seperating wedge between everything and everyone. Good v bad. Interestingly enough, Genesis establishes the foundation for the bible with this seperation with it's metaphors for adam and eve, satan and god in eating from the tree of knowledge. (Why does the bible use metaphors? Why do people try to take a litteral understanding when reading out of context? This is why there are thousands of religions from one book. Because in the metaphors lies room for misinterpretation and it's these reasons why i believe the bible is a manmade creation because in it's very root, it seperates i from god. Everything made more sense once i got past that. The whole we're all hydrogen blah blah... I've digressed.)
When you take that state and then make everyone responsible inside a religion or cult for their own individual fight in the doomsday race against time where how you conduct yourself along the way is judged by peers, and judicial persons, the individual is constantly in a place of survival from the bombardment of the mind asking "am i good enough" "will i survive". The prolonged effect of being in this survival state kicks in coping mechanisms and some deal with it better than others. Some fall into self loathing from not feeling good enough, some feel they're doing better than anyone else or lie that they're doing better than anyone else. Depression, split personality, narcissism etc. are all symptoms of the coping with one's situation by oneself in a setting where they don't really understand what's going on or what will happen. So basically, when i see a narcissist, i just see a person whos been exposed to an experience where they had to find a way to cope and survive. I often feel narcissists have it better than the other route which i suppose is self loathing. Whichever way we look at it, i feel the very root of mankind's identity crisis is rooted in the seperation of everything. But then again divide and conquer wins wars!
These are just thoughts off the top of my head and i went off topic and rambled. Sorry about that. But when you type on a tablet it makes it very difficult to delete what you've tapped out with one finger! Did i write anything that made sense? Or even connected to the topic?