~Tulku Urgyen Rinpoche
Everyone agrees that the body, speech and mind of living beings are constandy changing, continually coming and going. Still, the basis of our ordinary body, speech and mind is the buddha nature, the dharmadhatu that encompasses all of samsara and nirvana. There isn't a single being for whom this isn't so.
Dharmadhatu pervades all of samsara and nirvana. It is essential to start out with a basic understanding of the profundity of what is meant here in order to be able to authentically practice the teaching of the Great Perfection. Unless we know what is what, at least intellectually, it might seem to us as if sentient beings are disconnected, alien entities, and we have no idea of where they come from, where they belong or what they actually are. They are not disconnected at all. The difference between buddhas and sentient beings lies in the latter's narrowness of scope and attitude. Sentient beings confine themselves to their own limited little area of samsara through their own attitude and thinking.