One of the issues with running in the “real world,” even one in which magic and elves and dwarves and orcs exist, is the question of the origin of divine magics. Hand-waving on this point is not an option, especially because a majority of the group (myself included) are staunch Christians. The idea of clerics wandering around casting spells in the name of Jesus is just a bit, well, too much, even in the context of a game.
Thus, I will here attempt to present the cosmology of the universe that my campaign world exists in such that clerics of any religion will be believable both in their faith, and in the source of their power.
We must start with the fact that there are extant powerful beings who enable the casting of a kind of magic that is separate from that which the arcane schools wrench from the fabric of the universe. This is not a difficult point to render believable. The Roman Catholic church has a traditionally held belief that each person is watched over by a guardian angel. I will utilize this precedent, and declare that each cleric has a particularly powerful “guardian angel” who has in itself the power to manifest the power required to energize the spells of the clerics.
My world exists because it is created. There is one ultimate source of power in the universe, the God of gods, the Penultimate Creator. From this being comes all power, energy, light, reason, and order. To lesser “spiritual entities” he assigns greater or lesser amounts of power and in some cases agendas. Below those middle managers are other less authoritative spirit beings that humans have recognized in various forms, some humans call them spirits, some call them angels, some call them oni. These spirits then, being recognized, are the “face” of the Penultimate Creator. The middle managers might be interpreted as various lesser gods, while the Penultimate Creator is greater in authority even than these. This being because he created all of them, and allows them power according to his own agenda.
Thus, the power which clerics wield is the power of the Penultimate Creator, filtered through several intermediaries into a standard form that is recognized as the cleric’s spell list. Humans, of course, can only be allowed to wield so much power at once, and as they prove themselves worthy of that power, their allotment is increased at the rate which is most beneficial to the development of the individual’s responsibility and morality at the discretion of the guardian angel and the overseeing spirit.
As for the planes, there is of course the Prime Material Plane wherein the world exists. There are also the four Elemental Planes, Fire, Earth, Water, and Air. Below is the Plane of Punishment, and above the Plane of Reward. Suffusing all of these to a greater or lesser extent is the Astral Plane and Shadow Plane, allowing travel to spiritual aspects of the residents of each plane. Outside of the Astral Plane is the Realm of the Creator, where the primary expression of said Creator resides and holds court, issuing directives and controlling the cosmos. While the basic, physical portion of creatures residing on the Prime Material Plane remains on the Material Plane, it is possible for the spiritual portion of sentient creatures to travel on the Astral or Shadow Plane to visit other planes, excepting the Realm of the Creator, which is inaccessible to all, except those spiritual beings who have been assigned the most power.
Oh, a note about Arcane magics: The multiverse was created according to rules and logic, and through research, experimentation, and the right kind of insights, certain individuals are able to manipulate aspects of the physical world to leverage these elemental laws in predictable ways that manifest in a way that humans call magic. So, instead of physics, my world has magic. It has physics too, but no one is going to devote much time to the study of it when things like fireballs and planar travel are available.
Is that about it? I think I’ve covered everything. If anyone has any questions about any of this, I will be happy to answer them. Comments welcome, as well.