One idea I’m surprised I’ve never seen some religion propose is that there is only one soul, endlessly reincarnated. For instance, every person (or every living being) has the same soul at some point in its progression. Perhaps the soul begins as the vilest human or the basest animal and slowly works its way towards enlightenment each generation. Then it becomes divine. Obviously this would involve a time traveling soul that could incarnate in ancient Greece and then modern China and back again. The advantage is that anything good or bad you do, you do to yourself, which is a powerful incentive if you believe. Downside is you’re Hitler.
