Astate that can only be ruled by people of royal birth follows which theory of the origin of the state?

The theory that you are looking for is "the Divine right theory".

This theory claims that only certain people who were given the divine right to do so can create countries and that royalty is supposed to exist as rulers, without being questioned.

Communicating with the dead was common, it wasn’t seen as bizarre or weird,” explains murch. “it’s hard to imagine that now, we look at that and think, ‘why are you opening the gates of hell? ’