I believe the spirit is the part of every person that is aware of its place in the universal order of things. The spirit, being part of the universal oneness that can be represented by Nature, God, The Force, or whatever other image we may concoct to describe that which is larger than our intellectual consciousness, IS always aware of itself and the rest of the cosmos, but sometimes the body and mind it inhabits are not.

The only way to allow our spirit to get in touch with the larger spiritual universe is to begin to satisfy the needs of the other levels of our consciousness: the physical, the social, the emotional. Only once these are satisfied or at least have been promised satisfaction will the spirit emerge from our deepest subconscious to remind us that there is more to existence than what our physical, gregarious, self centered feelings demand.

In bdsm the need to be one with our partner or partners or existence in general in sharing feelings, emotions and sensations that go beyond the "normal" (I would say traditional) wants of more average relationships could be considered a spiritual need.