There’s a possibility that Fullmetal Alchemist Brotherhood was telling the story of how:

— parallel realities/universes/dimensions are real

— the leaders of our world are satanists willing to sacrifice the souls of their peoples to satisfy their own lust for power

— the energy around us can be accessed and used to produce whatever we desire, we just need to learn how to tap it

— the search for Truth is the search for God

—symbols are meaningful

— souls are a type of energy, and therefore cannot be destroyed, but can be captured and used

— what goes on in our world has real effects in our neighboring universes/realities/dimensions