We're all familiar with the Golden Rule: "Do unto others as you would have them do unto you." It famously suffers from the problem that others might have wildly different preferences from you. This has lead some to propose the Platinum Rule: "Treat others the way they want to be treated." That seems an improvement, though of course you can't give everyone what they want, and doing so wouldn't always even be good for them (say when people have ignorant or self-destructive desires). Still, I think the underlying idea here could be captured even better by what I will call - for want of a more sensible name - the Plutonium Rule: "Treat others as you would in the knowledge that you will one day be* them." Complement this with my theology of choice and you won't even need the hypothetical.
* = (I guess it's kind of like a really big mutation.)
Seriously, it seems like the sort of principle you could live your life by. And it really would be nice to be able to believe the theological underpinnings. (It's so much cooler than all the other religions I've come across.) One's sense of shared humanity could be significantly augmented by a sense of shared divinity. You would "belong to something greater" than your (mortal) self in a very literal sense! This satisfies some very basic human yearnings. But even if you don't take it literally, the heuristic value of the hypothetical strikes me as pretty significant. It really helps you (or, at least, me) appreciate the striking reality of other people, empathize with their concerns and aspirations, etc., in a way that can be difficult on the usual way of thinking which sets oneself apart from others.
The heuristic naturally leads to the sort of moral theory defended in my 'Consistency and Utilitarianism', which I find pretty plausible. It's not brute preference utilitarianism, because I really don't want my future fundamentalist other-self (say) to have his theocratic preferences satisfied. Far better if he/we could be given the opportunity to become more enlightened. (I expect he would want the same on ideal rational reflection, so an idealized preference utilitarianism might yield the same results.) Similarly for rehabilitating criminals and such. In general, the plutonium rule should remind us of how important it is to enable others to improve themselves and realize their full potential.
The rule may also help us to resolve puzzling questions about the total value of humanity as a whole. Consider the population paradox. We should not be pure aggregators, since we wouldn't think that living a zillion lives of barely-above-baseline welfare is all that wonderful. But nor should we accept a purely 'averaging' approach to value theory. If you could live another life, still very worthwhile but just below the average utility of your other lives, then that sounds like an opportunity worth accepting. (Doesn't it? If you disagree about this then you could be an averager, I suppose.) So, trade-offs and discretion are required. In general, we might evaluate a possible world by asking how you'd like to be the immanent 'God' of that world, living each of the lives contained therein. The best worlds are those that we'd most like to divinely experience (on ideal rational reflection). Sound plausible?