There is a great deal of scholarly knowledge surrounding ancient cultures and how they managed to function. Particularly in pre-literate societies, not only did laws and regulations, but societal norms and customs, had to all be passed down orally. Just as importantly, they had to be remembered and not forgotten to be passed down to future generations. How does non-literate society impress upon it's members that the stories they share are important enough to be remembered and re-shared? They are done under the guise of religion and either as edicts from the gods, or as stories about the gods.
The ancient Greek and Norse both believed strongly in treating strangers and travelers as honoured guests, for one could never be sure if the traveler wasn't Odin or Zeus, who often did travel amongst the mortals.
An old story about the Jewish prohibition against eating meat from hooved animal claims that the root source is due to that particular type of meat not being safely storable. Regardless, eating bacon became ingrained in Jewish laws, and probably would have been ignored if it did not come from God.