All themes must adhere to this. If they cannot adhere to it, they must adapt to it. If they cannot adapt to it, then the theme in general is disallowed.
The universe, for the purposes of this MUSH, is comprised of an infinite number of dimensions organized into clusters. Travel between the clusters is, obviously, possible, and it seems that a good deal of the dimensions of this MUSH have compiled themselves together.
The universe has two very powerful beings at the helm. The first is the ruler of the universe, the compiled, omnipotent, sentient, omniscient and omnipresent force of Good. Mortals refer to It as a myriad of things, but 'God' or 'Creator' is a close enough summary. It created the universe and apparently has plans for it. Though benevolent, It rarely interferes with the affairs of mortals, usually only acting through them or subtly influencing the universe. Only advanced races have absolute proof of It's existence, and little else to confirm. It's opposite number, of course, is the less powerful, but still influential combined force of Evil. 'Satan' is a good enough approximation, and it wishes ill to the children of the Creator. Again, however, it only rarely directly interferes with the affairs of mortals.
Below each of them are pantheons of angels and demons, respectively, bound to the service of their master, both by their own will and nature of their creation. Then there are the gods and demigods, beings of great power comparable to angels and demons but not necessarily aligned with either the Creator nor Satan.
All sentience and most higher-level consciousness requires a soul. A soul becomes bound to the physical phenomenon required for consciousness and sentience. This is independent of the medium - a robot can have a soul just as easily as an organic being. Souls have a certain amount of influence on the world around them, and awareness of other souls, which manifests in magic and some kinds of psionics (the other psionic types being related to neurological structure). At death, the soul lingers about for a while, often in the beginning stages of entering it's eternal resting place; however, for a limited time period (usually no more than a few days), if the conditions are right, a soul can be returned to it's body or transferred to an appropriate alternate host. The details are sketchy, however; there is no real science as to how long a soul can be retrieved or what kind of medium is appropriate for their retrieval. Reincarnation is known to be possible, but it's frequency is relatively unknown, nor it's purposes in the greater scheme of things. Most reincarnated beings do not retain a memory of their past lives, but usually retain the same personality in general, and often can have parts of their past lives or memory restored under appropriate circumstances.
The realms of the Creator and Satan are Heaven and Hell, respectively. The Creator is the ONLY one who may judge who enters these kingdoms (though some say that the deceased actually judge themselves for their deeds). Various Heaven-like and Hell-like dimensions exists, often in some way connected to the real thing, with false angels and demons - not necessarily working against the real thing, but sometimes pretending to be such. No living mortal may enter either place directly, nor may they be taken there while alive. Most Heaven and Hell-like dimensions are extremely difficult for non-native mortals to enter, as well, with almost all of the Hell-like dimensions killing the mortals in the process.
Mortal souls can be stolen; however, this does not imply that they go into Hell. This merely means that they cannot move on to the next stage in existence until they are released. On occasion a stolen soul is a good thing, as it allows potential rescuers to resurrect an otherwise irretrievably dead individual. Soul stealing, though extremely powerful, tends to come to haunt back the user and is EXTREMELY difficult to do. Lesser versions, such as stealing spiritual energy without removing the soul, or gleaning energy from the release of a soul (i.e. at a sacrificial rite) are much easier, but usually also come back to haunt the user, due to their habit of trifling with things which were not meant to be toyed with. Souls CANNOT be destroyed under any circumstances.
At this MUSH, the Creator, Satan, true angels, true demons, and most gods and demi-gods are INAPPABLE. If the theme in question has, for instance, angels or demons, you will probably be able to stick them in the 'false angel' or 'false demon' category and app them that way. Further, if your theme is ruled by other gods, typically they can work as the gods or demi-gods listed here. However, all characters must comply with this arrangement, albeit they may not appear to on the surface of their theme