A soul is often thought of as being the "real" person that survives the death of the physical body, that may or may not be a hologram of that person's latest physical form. The essence of the idea is that identity and memory pass from the body to heaven or from the body to a new body. Sentience remains within this invisible electromagnetic form. And this is an Eastern philosophy learned in Tibet by one Yeshua of Galilee who took the philosophy home with him and eventually got hung by Roman soldiers for his efforts. They tell us that a body cannot be sentient without receiving a soul from wherever. I'm interpreting this rather broadly, most of these philosophies talk about the souls coming from some invisible realms where the people may have forms analogous to physical bodies, or not as the case may be. Then they tell us that the soul is more important than the body, and that its needs come first. Isn't this exactly like the actions of a parasite? Without regards to its host a parasite consumes what it needs, grows and eventually leaves the host when the host dies. It may or may not reproduce within that host, and it may or may not be able to survive the death of its host and infect another. It has occured to me more than once that the relationship can be either parasitic or symbiotic. A parasite takes without giving back. A symbiote provides something that the host needs while the host provides it with room and board. Since the soul is allegedly the seat of human sentience, a parasitic soul might be thought of as the kind of soul that continually makes decisions that are bad for the body. Two versions of this have been popular. One is drinking, smoking, and having sex for pleasure, which I think feeds the soul just as well as the other, which is "mortifying the body" in some way or the other that satisfies religious requirements. There is the idea in a parasitic relationship that the parasite actually has to cause harm to operate. The lines are never that clear. If a parasitic soul contains any sort of sentience, it would be advantageous to the survival of the host. A soul that is too self-sacrificing might even unconsciously work against the interests of the host by not having enough of itself involved in the current reality that it can help the host to survive. And maybe this all just consists of what the person has learned as he or she grows up. Even so, the learning and the self-image that a person has been taught can be parasitic or symbiotic or some mix.