(Educational profit, that is.)
I've written a lot about religion over the past year. In one of my more methodological posts, I argued that religion is not about beliefs. The beliefs may be crazy, loud, or otherwise salient, but they're a distraction if your goal is to understand the phenomenon of religion.
It's especially distracting to engage with the beliefs on their own terms. My advice was to ignore them:
Don’t worry about the beliefs. Ignore them. Better yet, put them in little clinical boxes with labels that say SPECIMEN, and tuck them away in your favorite filing system. Then you can start to make progress on the really interesting questions. (And maybe, after that, go back and reconsider the beliefs.)
Today I'm going to re-engage with some of the beliefs. But I still think it's important to maintain clinical distance — to take the outside view rather than the inside view.
To that end, I'd like to propose two related thought experiments — two ways of getting at the phenomenon of religion from an 'outside' angle.
1. The God Experiment
Imagine yourself the god of a large, early-historic tribe. Your task is to design a religion, and you have only one goal:
Gain as many loyal followers as you can over the next millennium.
But there's a catch. You aren't an omnipotent god, or even omnipresent. In fact you have only one supernatural power: you can program the minds of everyone in your tribe. Once you've exercised this power, you vanish in a puff of smoke.
So use it carefully. Whatever choices you make, the current members of your tribe (generation zero) will abide perfectly. However you want them to behave, they will behave. Whatever you want them to believe, they will believe. But after that it's hands off, and you'll have no other chance to influence the world. Later generations will learn about you only through the natural, secular forces of cultural transmission and evolution.
Your goal, remember, is to gain as many followers as possible. You are playing the long, long game.
So what kind of god will you be?
Here are a few questions to get you started:
- Will you demand loyalty and obedience?
- Will you be a jealous god, insisting that there be no other gods before you? Or will you be a permissive god, allowing your followers to worship others as they see fit?
- Will you demand devotion on a weekly and/or daily basis? (I recommend both, but it's up to you.)
- How many times a day will you ask for prayer? Will you make it open-ended, or specify a number? 50? 10? 5? Once before bed?
- Will you ask that people gather together to worship you? When they do, what activities will you encourage? Chanting? Singing? Holding hands? Praying silently? Eating? Playing marbles?
- Will you require public displays of devotion, like oaths, sacrifices, and other conspicuous rituals?
- Will you make periodic holy days, so that your people — even those who skimp on their daily and weekly devotions — will be reminded of their duties to you?
- You'll probably want some scriptures, yeah? Don't tell me you plan to rely on transmission by word of mouth alone.
- Will you weave a compelling narrative for your people, one in which they are privileged, blessed, or chosen? (This may help them feel closer to each other.)
- Will you cultivate a professional priesthood — a class of people who specialize in worshipping you, and who teach and encourage others? How will you make sure they don't abuse their privileged position?
- When these professionals preach in your name, would you like them to drone on in a language few can understand? Or would you prefer some charisma, delivered in a language of the people?
- Will you require celibacy of your priests? (If you let them have children, it will split their loyalties between you and their genetic offspring.)
- Will you allow women in your priesthood? Why or why not?
- This seems like a no-brainer, but I'll ask anyway: will you require that children be brought up to worship you?
- Will you require marriage for the purpose of raising children? Will you proscribe sex before marriage? Will you allow polygamy, or require monogamy? Will you discourage homosexuality? Why or why not?
- Will you preach duty to parents? To the whole extended family? To distant ancestors?
- Will you prescribe rules and roles for the members of your chosen tribe, so that they might live together more harmoniously?
- Will you ask that your followers evangelize in your name?
- Will you offer eternal life or perfect happiness, to lure converts?
- Will you threaten eternal punishment, to deter defectors?
- How will you instruct your tribe to treat apostates and heretics? What if someone is claiming to be another god (or claiming to be you!), and gaining lots of followers?
- Will you be a god of peace or a god of war?
- How will you instruct your tribe to treat outsiders? Should they be completely open, or wary and closed off? Or aggressive?
- How will you allow converts into your tribe/religion?
- Will you require that your followers maintain a strict code of dress and conduct, such that they might more easily recognize one another and distinguish outsiders?
- How should your tribe treat its poorest, weakest members?
- How much will you allow the powerful among your tribe to oppress the weak? A lot? A little? None at all? More pointedly: do you even have a say in this? How would you go about it?
- Will you allow your followers to submit to their earthly masters (to render unto Caesar what is Caesar's)? Or will you demand that they recognize no authority but your own, in matters both spiritual and temporal?
- How much power will you claim to possess? Will you offer a realistic assessment of yourself (as a one-shot wonder), or would you prefer your followers to think of you as all-powerful, all-knowing, ever-present, and eternal?
- Will you allow your tribe to make images of you, to worship you by proxy? Why or why not?
- What happens when your tribe falls on truly difficult times? How will you ensure they don't forget about you when worldly concerns become a matter of life and death (when they're ravaged by war, famine, drought, disease, etc.)?
- What happens when your tribe is extremely successful (in material terms)? Is decadence a concern for you?
- What other cultural mechanisms will you use to reinforce all of these decisions you're making? What kind of art will you try to cultivate? What kind of intellectual culture will you encourage among your people (especially your priests)? What kind of rituals would you like your people to enact? What institutions would you like to develop around your religion, to preserve and reinforce your messages?
- Here's one you may not have considered: How will you handle spiritual/ecstatic/transcendental experiences? There are extremely powerful psychic forces at play in these kinds of experiences, and you'll probably want to co-opt them, somehow, for your own purposes.
There are plenty of other decisions you'd have to make (if you were actually playing this game), but I've gone on long enough. That should be enough to give the flavor of the thought experiment.
Of course, some of your decisions will depend on the specific context in which your tribe finds itself. A god-strategy optimized for a large, powerful, agricultural tribe might not work well for a smaller, weaker, nomadic tribe. A strategy that works for a god of the desert might need tweaking for a jungle god, river god, or island god. If your tribe is situated in a region with many competing ethnic groups, you might find it necessary to treat outsiders differently than if your tribe lives in a more homogeneous region. If your tribe has recently flourished, or lives by itself on an island, they won't need as much help thinking of themselves as special or set-apart. Etc.
The point here isn't (necessarily) to come up with concrete answers, but rather to think about the design exercise itself. What factors are relevant for determining how successful you'll be? What sub-goals will inform your overall design? 
You might want to break your strategy down into the sub-goals of fidelity, fecundity, and longevity. These are the three important components of any evolutionary strategy, e.g. biological replicators.
- Fidelity — you'll want to preserve your doctrine/concept/religion as faithfully as possible, so later generations will abide by your original intent as much as (humanly) possible. Fidelity mechanisms include scriptures, punishment of heretics, reverence for ancestors, etc.
- Fecundity — you'll want your religion to spread to as many minds as possible (which is your explicit goal, after all). In the name of vertical transmission, you'll want your followers to make as many babies as possible, and you'll want to pay special attention to their indoctrination. In the name of horizontal transmission, you may want to encourage traditions of evangelism and/or military conquest.
- Longevity — you'll want both your religion and your tribe to live as long as possible, especially since the tribe embodies all the cultural, structural, and institutional mechanisms for enacting your strategy. To that end, you'll want your followers to have high solidarity (so they will work together as harmoniously as possible). This is where morality, ethics, and politics come into play. Schisms probably aren't going to help your cause, and though they may be inevitable, you'll want to mitigate their effects (e.g. using various fidelity mechanisms).
Another sub-goal is to get as much 'running time' in the minds of your followers as possible. Periodic reinforcement can help a lot here, through the effect known as priming. The more recently and more often a concept has been active (in a human brain), the more likely it is to become active again in the future.
Daily, weekly, and yearly (e.g. holiday) activities are one way to prime concepts that are important to your survival as a god. Rituals are important too — and very sticky. Because rituals are structured, formalized, repetitive, and kinesthetic, they are perfect units of teachable/learnable behavior. And when rituals are connected, ceremonially, to an important religious concept, they serves as powerful body->mind priming devices.
Anyway, my point here is that the more time and effort people spend on you — especially conspicuous/public effort — the more primed you'll be in their minds. This makes you more likely to spread to other minds, and more likely to endure through periods when you aren't as relevant to the tribe (or to individuals or subsets within it).
2. The Tribe Experiment
Now let's imagine a second thought experiment, similar to the first but with a slightly different premise.
This time you aren't a god — just a wise consultant. The elders of the same large, early-historic tribe come to you and ask for help devising a strategy that will enable the tribe to flourish, demographically, over the next thousand years. They believe — based on evidence from the past and what seems to have worked for other tribes — that a "god" concept should form the basis of their tribe's strategy. Their ultimate goal is survival and reproduction (demographic and genetic flourishing), but they think that promoting the idea of a god is a useful intermediate goal.
(In fact, the elders aren't particularly literal about this god concept, themselves — they prefer to substitute "the tribe" or "our society" whenever they hear or read about "god." For example, they would read the sentence "God is great" as "Our tribe is great.")
So, having been retained by this tribe to craft their god-concept and their religious beliefs and practices, what kind of "god" will you be?
Your goal, remember, is not to infect as many minds as possible with your religion (although that might be an instrumental goal), but rather to ensure the long-term demographic/genetic success of the tribe.
What's the difference?
Now here's the real question I came here to ask, the question I think is most illuminating:
How should your strategy differ if you're playing the God Experiment vs. the Tribe Experiment?
For the sake of argument, I'll put forward the thesis that there is no difference. Though the two experiments have different ultimate goals — survival and (memetic) reproduction of the religion vs. survival and (genetic) reproduction of the tribe — they are surprisingly convergent in terms of instrumental values (intermediate goals).
As a god in the God Experiment, you don't really care about the worldly success of your tribe. If you spread to another tribe, you'd be just as happy. But if your tribe dies out before you make the leap, you'll die with them. And the success of your original tribe is a pretty useful way to end up spreading to other tribes, whether by conquest or cultural dominance. No one is going to copy the religious culture of a weaker tribe.
So the God Strategy seems to be a strict superset of the Tribe Strategy. What's good for the tribe is good for the god.
But what about the other direction? Is what's good for the god necessarily good for the tribe? If so, why, and if not, where's the disconnect?
You might think that "spreading your religion to other tribes" is an example of something that's important to the God Strategy, but irrelevant to the Tribe Strategy. Whether other tribes worship the same god shouldn't affect the survival and reproductive success of your own tribe, right?
But consider the benefits. Tribes that share a common religion are going to be much more aligned than tribes that don't. Religion isn't (just) about belief — it's also about culture. A common religion gives people in different tribes a shared frame of reference, shared values, shared language, and a shared narrative (of where they came from, who they are, and where they're going). Tribes that share a religion are, ceteris paribus, less likely to go to war with each other, and more likely to band together to fight outsiders. They're more likely to merge into an even bigger, more powerful meta-tribe. (This will blur the demographic lines that are important for the Tribe Experiment, but descendants of your original tribe are going to have the DNA you care about whether they're mating with insiders or outsiders. Your goal in the Tribe Experiment is to make as much of that DNA as you can, regardless of where it ends up.)
Katja Grace notes that goal-directed agents benefit whenever other agents share the same values. Our tribe surely qualifies as a goal-directed agent (even if its agency is a bit decoherent), and would similarly benefit from other agents (tribes) sharing its values.
Maybe the only difference between the God Strategy and the Tribe Strategy is one of emphasis. A god will care slightly more (than the tribe does) about spreading to other minds, and slightly less about the tribe's demographic/genetic success. But the differences are at the margins; overall, there's strong alignment.
In other words, the relationship between god and tribe is symbiotic rather than parasitic.
 Since this is a design exercise, it's critical have a solid understanding of the constraints of the problem space. You will, of course, have to take the physical world as given (sorry no miracles). You'll also want to understand how the natural world affects the meat-based brains in which your message will live. This includes disease, death, famine, etc., and all the economic and ecological constraints that every species will encounter. Much more important, however, is to have a deep understanding of human nature — of the psychological, social, and political realities your message will face as it gets transmitted and transmuted across space and time.