I’ve always been fascinated by books and campaign settings that give earthly explanations for mythology and the divine. I think it really adds to the story when you can explain the divine within the rules of the game or what is known. Two of my favorite trilogies do this: The Legends of the First Empire by Michael J Sullivan and Troy by Devid Gemmell.
Gods play a huge role in tabletop role playing games. They grant spells, they provide a source for evil and good, and they provide a moral focus for many divine casters. They also provide a way for writers and DMs to hand-wave difficult situations or explanations, but what if there were no gods? How would the characters get their divine spells? Know good from evil? How would divine intervention be handled? The Forces and Philosophies religious system provided in the DMG explores these questions.
This religious system is all about channeling divine energy based on the conviction of the channeler’s belief. With this system, a character can believe in a rock and still cast divine spells; however, a rock isn’t very interesting to build a character around, and it doesn’t allow for the divine intervention scenario a DM may need from time to time. How about an ancient dragon that has lived in a volcano for over a thousand years? Once every human generation or two he probably made an appearance and devastated the region, causing all kinds of lore about an angry god who punished the people for their transgressions. Alternately, maybe the dragon took an active role in the lives of humanoids and guided their growth and culture to suit his needs. Either way, you can build a dogma around this and have divine characters that believe the dragon is the one granting them their spells.
What about the divine intervention scenario? Well, divine intervention can be a lot of things. It can be blind luck, it can be the subject of worship taking an active role and interfering, or it can be angels taking an interest and helping out. With the absence of actual deities, it doesn’t mean that the upper and lower planes don’t exist. They do—they are just more mysterious. They are more like what heaven and hell are to us in real life, a thing of story and belief rather than a known fact; for instance, when a giant cleric posing as a god to a short-lived race uses a spell that summons an angel to assist one of her subjects giving prayer, that can be construed as divine intervention. The reality is, however, that the giant has her own belief that allows for her to channel divine power.
What happens when the character learns the truth? Eventually, your character will grow to be as powerful or even more so than the creature worshiped as their god. Does that mean your character will lose their ability to cast divine spells? No, it just means they came to a new understanding of the cosmos. They now know that their spells are granted by their conviction, which only serves to make it stronger. What if they start spreading word that the god isn’t a god? So what! How many different beliefs exist today about heaven, hell, and the creation of the world? Even with all the science we have, religion still has a strong hold on our society. A few naysayers aren’t going to dispel generations of tradition and culture.
Using the Forces and Philosophies religious system allows for a lot of great storytelling. You can actually have characters fight and defeat gods or even become gods themselves. You can choose if the object of worship is a creature, an object, or a philosophy. It also allows for very interesting origin stories and gives a possible explanation as to why a city of giants doesn’t interfere with the growing nations of humanoids directly.