Why did the playwrights chose to include supernatural forces in their stories?

A recurrent motif in the play is the presence of supernatural phenomenon and supernatural beings. For example, Harper and Prior met in a dream while they both think that the other person is a fragment of their imagination: Harper believes that Prior is her hallucination and Prior believes that Harper is just a fictive person that appeared in his dream. This proves to be inaccurate as both Harper and Joe reveal details about themselves that the other person couldn’t have possibly known. Most supernatural elements are linked with Prior and other characters like Harper who have some type of health problem thus highlighting the idea that normal people who obey the social rules can’t get in touch with what is beyond our world.