The film narrative centers on Satan impregnating Rosemary, a married woman in New York City. According to Roman Polanski, the film’s director, the decisive point is actually that neither Rosemary in the film nor the film’s viewers can know whether it was the devil who impregnated her. Beyond the more matter of being able to distinguish a psychosis from a more “objective” or external religious event, the importance of the supernatural to religion is also, albeit subtly, in play, according to Polanski.
The full essay is at "Rosemary's Baby."
