From WoD Gotham
One of the most rewarding and challenging aspects of role playing in Vampire: The Masquerade is discovering and playing out the relationship between the vampire and that of his Beast. Every vampire, whether neonate or elder has residing in him an entity known only as the Beast, it is named aptly so because of the animalistic urges it causes in the vampire's psyche, occasionally controlling the vampire through frenzies, when the Beast takes over the Kindred's mind and acts out its most vile urges to kill and destroy. Another aspect of the vampire and the demon inside of him is the Beast's slow, but inexorable control of the vampire's body as well as his mind. It does this through the loss of the vampire's Humanity. Many role players online and off see vampires as nothing more than ultra-powerful killing machines, capable of doing nearly anything and living forever.
This is the popular connotation of society's view of the undead. However, White Wolf has re-invented the myth of the vampire to evoke a more tragic aspect of being unliving. To better understand the vampire and that of his Beast, let's take the following scenario. You have just been Embraced, you are now undead and have capabilities only dreamed of by the ken of mortal men. However, inside of you is another personality, an almost alien force that whispers to you in your sleep and even during your waking hours. It whispers that it wants to be fulfilled, that it needs to gorge on the lifeblood of humans, or it will control you, and make you do acts that would revile the wickedest of mankind. This other personality inside of you is eating away at your conscience, every night you wake you find yourself losing more and more control of yourself. Deep down inside you know, that eventually this thing in you will take you over, you will forget who and what you are, you very identity will be wiped away, and this alien force will control you fully, and here is the tragic part: there is NOTHING you can do to stop it. The most a vampire can do is to satisfy the Beast inside, to give in to its wishes temporarily, so that it will sleep and give the vampire some time away from its control. But this only makes the situation more tragic, because by giving in to its wishes to vampire is only prolonging the struggle. We as humans cannot really conceive of the loss of Humanity as vampires suffer it. Imagine that the simple act of reading a book, or laughing with your friends, or taking walks on the beach no longer bring you enjoyment, it's now just an empty act that is meaningless next to the one thing that satisfies you: BLOOD. This is another aspect of the Beast taking hold.
This is the true aspect of role playing Vampire. It isn't about getting a level 5 in Protean or Thaumaturgy, that mechanical stuff is only there to make it easier for the players understand the game setting more. The true point of understanding and playing Vampire is to get a tragic and horrific feel for the loss of Humanity and how it relates to us in the real world, how no matter how powerful we become, we must always remember to keep and preserve our Humanity, which is ultimately, the most precious thing we have, and that it is very easily lost to our own inner demons. Vampire is indeed an eternal struggle, but not for Jyhad, or preventing/causing Gehenna, it is an eternal struggle for the soul.