In my System/World of Elthos I have it posited that the Gods (aka Elkron) are actually real. They are personifications of Metaphysical Realities. As such they command huge amounts of "Kismet" which is mystical energy, and with it can commit acts of Creation (or more accurately, Transformation, but that's a bit of a quibble). They, like Tolkien's Valar, create the world, it's terrains, and races, and so on. So they definitely exist. However, by the time of the Heroic Age, they've largely retreated from the world as they reserve their Kismet for the God War to come. It is during the Heroic Age that the Campaigns and Adventures take place for the Player Characters. So there's a huge back story about the Gods and how they created the world and why. The PCs play within the context of that back story. They may even influence the future if they happen to complete any of the Seeds of Destiny Quests that the Elkron setup during the Dawn Age... those Seeds of Destiny are like a Kismet gamble for the Elkron - if they are completed then they get a massive payout in Kismet, which again, they will want to use for the End of Ages (aka God War) at the end of the Great Celestial Cycle. Winning the God War establishes one of the Elkron as supreme over all others, making them the Lord of the Gods for the next Great Cycle.

So, magic and clericy in my world are linked in that they both use Mystic Energy. But one group, the Magic Users, use the Mana Energy that is intrinsic to themselves and gleaned from their environment, an can be augmented via certain actions or artifacts. Clerics on the other hand directly appeal to the Elkron to commit acts on their behalf. So when a Cleric invokes a miracle, they use their Mystic Energy to send out the call, but the act itself is performed by the Elkron, meaning that the effects can be larger scale then what individual Magic Users could perform, so long as the Elkron is willing (and able) to perform the action. In most cases they look relatively the same, in so far as invocations are specific and do specific things (pretty much like magic spells, but are specific prayers, aka Invocations). However, the potential for clerical effects are vastly higher than what an MU could contemplate. On the other hand, some MUs elect to be sorcerers, which is harder and slower in terms of progress than regular MUs, but they are able to master vast quantities of Mana, and are also able to make deals and arrangements with the higher powers (via magical contracts), and even the Elkron (like Circe in Greek Myth). Thus in the end a high level Sorcerer can become just about as powerful as a high level Cleric. The main distinction between the two is that MUs are using their own will and shaping the Mystic Energy using their Ego, while Clerics are calling on the Elkron to take actions on their behalf. That said, this does not necessitate that other Players of the Elthos system have to do the same at all. It's a very flexible system, and some GMs using the system do not even have Gods, or Magic (or the magic they have is very low powered compared with what most RPGs have). However, the configuration I have for Elthos has helped me to create a back story, and symbolism, that works for me as a GM.