[@Oak7ree] Thought I had: What if there was some evil force that was in constant war with good, both are primordial forces in the way of universal balance. These forces are generally at balance to some degree with advantages that wax and wane regularly but whenever one side successfully conquers the other (ie Good triumphs over Evil or Evil triumph over good), the world is destroyed and reborn anew.

In the process, great heroes and person from the previous world will be reborn as gods. Typically only the side that looses will get new gods so if notJesus beats notSatan, then Satanist Cult Master Jim will be reborn as notSatan in the new world but the original notJesus will still be around. I should probably mention that each "rebirth" would be several hundred if not thousands of years apart.

I feel like there should be a catch though that Good isn't saintly and Evil isn't terrible but instead two different aspects of Order and Destruction respectively. Order is needed to build civilization and develop things but at its apex, it will force everyone into a Grand Plan which does not allow for any flexibility while Destruction leads to anarchy and living in danger at its peak but it is also what grants beings free will.