Just sharing some of my thoughts about this separate entity from the physical body - "soul" or "spirit". From what I understand about Buddhism/Dharma, the Buddha is quite against the "idea" of presence of an eternal entity as soul or which can be "craved" as a "self" or "atman" in this body-mind that makes our existence. The emphasis on "anatta" - "non-self" of Buddhism is coined to oppose this idea of permanent soul. This is an object of craving, and which prevents us from seeing the selfless nature. The concept of presence of "Buddha nature" has to be understood from this selfless principle of original Buddha's teaching. Peace.