If you do not at some level believe in that then making progress on the path, standing up to all the challenges we face from our thinking mind and our environment, would be very difficult if not impossible. For it is to your true Buddha nature that you turn your life over to, that you surrender your ego thinking-mind to, that you find refuge in when you are present, free of the intervention of thought. Your true Buddha nature is your “not self,” the antithesis of your ego. It is your source of strength.
As we progress on the path, we make more and more conscious contact with our true Buddha nature. We experience its wisdom, its seeing with equal mind, its freedom from likes and dislikes, its awareness of the emptiness of all five skandhas.
And if we are lucky, at some stage in our practice, we become one with our true Buddha nature 24/7. I am not there yet, for that is enlightenment, that is complete freedom from our ego thinking-mind. that is freedom from all fears and obstructions, from all confused illusions.
And so belief in your true Buddha nature is both the beginning and the end of the path, in the sense of having made it home. The path itself, of course, has no end; it continues till we die.