My assertion is that body/soul/spirit is a reflection of the 3 persons of the Trinity. It helps me understand the Trinity better because I can see my spirit as a separate person that sometimes makes me do things I don't understand, but my spirit is not a separate entity.
The soul can have a carnal greedy will of its own, psychikos in Greek vs psyche/soul. The spirit/pneuma can lean towards pneumatikos, spiritual wisdom and ultimately spirit body in the Resurrections. Those who have unclean spirits probably had something wrong with their spirit, to begin with.
Clearly, they have a consciousness of their own since they survive death. I assert they have a will of their own as well. Having sentient consciousness with a will is a good description of our physical state, that I would argue applies to all three aspects of our being.
That makes me feel like the Trinity is an intuitively obvious truth if you put it in a certain light. I feel inspired by believing that it is so fundamentally true that it can be derived from intuitive deduction.
This has two problems:
1) It intimates Modalism, by denying the real distinction of Persons in the Trinity.
2) It assumes trichotomism, a strict division of the human person into three parts: body, soul, and spirit.
The problem with the Modalistic issue, should be obvious.
The issue with trichotomism isn't that it is necessarily false, so much as it isn't necessarily true. Scripture instead tends to speak of human beings as having a material dimension as well as a spiritual dimension. Ideas like "soul" and "spirit" are not well defined, nor are they even necessarily to be understood as different things at all. Many look to the passage in Hebrews which speaks of the word of God as living and active, even cutting soul and spirit and assume this means the soul and spirit are entirely different things. But the text doesn't really suggest this, as the meaning isn't the cutting of the soul from the spirit; but rather cuts even the soul and spirit--the most interior things of man, as the author also speaks of the joints and marrow and the thoughts and intents of the heart. The word is so sharp that it can cut asunder, even the deepest things.
Even moreso, to speak of the "parts" of man can also be manifold, indeed we must also speak of the mind, the will, the heart, etc.
I am personally drawn toward the idea known as the psychosomatic union, that is, man is a union of body and soul. The body is the material dimension, the soul the immaterial--the will, feeling, conscious thought, even the animating principle of the body. The body without the soul is a corpse, and the soul without the body is naked. God created us to be these things together, "then the LORD God formed the man of dust from the ground and breathed into his nostrils the breath of life, and the man became a living creature." (Genesis 2:7). The absence from the body that arises from bodily death is an unnatural state, one that happens because of the fallenness of the world. That is why we look forward to the resurrection of the body in the Age to Come, when God makes all things right, restores all things--this is our future and glorious hope.
-CryptoLutheran