Soul
A soul is an item of immense power. Individual willpower, unconstrained by the flesh, it has the power to reshape reality.
When a person dies, their soul finds a 'home' that produces the most harmony with their spirit. Some dimensions welcome new souls, and there are many gods and goddesses of death who are charged with escorting those souls into their ranks. Such souls enjoy an eternity as an abstract spirit in that demesne, while others might be reborn into the living population. Because each new soul grows the power of the dimension, the gods of Olympus and Asgard have jockeyed prominently for followers. If a person is impressed with the ideals expressed by the existence of a place while they are alive, their soul is more likely to be attuned to that place in death. But just as a warrior might be drawn to Asgard, a cruel person would be drawn to Hell, as it is the truest reflection of their innermost self.
It is when a soul has reached a state of completion-- Nirvana, perfection, serenity-- that the soul may be drawn towards Heaven. If there is a purpose to souls, it is to preserve knowledge between lifetimes until that spirit is complete. Only then can someone transcend to the next level of awareness.
There are two agreements that must be obeyed: A Soul cannot be destroyed, and a soul cannot be taken without consent. Attempting to destroy a soul is considered an act of heinous barbarism, because it lessens the total amount of power in the universe. Such an act requires the darkest of black magics, a blasphemy on scale with opening the gates to the Realm Between Worlds.
Capturing a soul without consent is the sort of offense that moves warfare on a truly cosmic level, mobilizing forces to march between the dimensional walls in full invasion. If it is fair game to simply take souls, then outright war would erupt and hoarding would begin. This is why contracts and Faustian bargains are so frequent; the spirit is giving full consent, even if it means that the spirit would otherwise be attuned to another location.
