The problem here is definitely language, some philosophy, and that we are not enlightened.
When speaking of Buddha Nature, we seem to give it an identity as something, a Self or self for example. But inherently it is empty of all yet and full at the same time. So no matter what we are speaking of, we always give it an imagination of what we think it is, and give it an identity as Self. The problem with Self is it sounds like a possession which Realized Buddha Nature is empty of such. But how can you not call it Self when it has these qualities and those qualities, and from it forms arise. How can you call it Self when it is inseparable from other Buddha Nature. Self in relation or comparison to what...the problem here is US, because of our attachment to define, dissect, analyze, and philosophize in trying to see or understand what Buddha Nature is. We forget that the only Buddhas and Great Bodhisattvas are able to see their Buddha Nature...remember Buddha and Bodhisattvas work according to our attachment but does not mean they are attached like us. So we are attached to language and words such as Buddha Nature, they will explain to us what it is..remember the core teachings of Buddhism is to leave attachment...our problem is we are attached to form especially language and words...because of our attachment, that is why there are many methods or forms that are being employed to help us such as Tantra, Chan, Pure Land, etc. That is why there are many Sutras and not One. When disciples asked, Buddha answered. And other times Buddha spoke about a particular Sutra without inquiry from disciples. What Buddha spoke is accord with sentient beings' attachments. Other times when people asked Buddha about something, Buddha answered.
For our sake, I will say Buddha Nature is the potential to become Buddha. What is Buddha? Cultivate the path to become one and we will know...But ultimately, if you accept Buddha Nature without philosophize or analyzing, then it is just Buddha Nature. In Taoism, it is called the Great Tao. In Buddhism we call it Buddha Nature. In Confucianism, it is called something (which I don't remember). In Hinduism, I will not say what it is called. But they all refer to the same thing...after we have questioned the teachings, and we now can accept the teachings as they are...In my opinion, Buddhism gives clarity to Taoism, Confucianism, and Hinduism in terms of theory and practice. In other words, Buddhism explains things, nature, phenomenons, universe, how we live, etc and how to practice in a clearer view than other traditions can.
But with a closer look, Hui Neng said Buddha Nature is when we don't think of good or evil, that's Buddha Nature or original face. It is not far or close. But the closest is right front of us is what keeps us moving, doing things, etc. Otherwise, we would like like a rock or a dead body. The calmer and clearer we are through practice, that is Buddha Nature...When Buddha Nature is defiled, its effects are what we are now in terms of consciousnesses, but without Buddha Nature the organs would be nothing more than tissues. When we die, what's left behind is the body.
Lastly, if you are still attached to learning more about Buddha Nature, here is a link to what I postedviewtopic.php?f=66&t=3985&start=60