In the New Testament, Satan himself quotes the psalm, and ever since, that text has both reflected and shaped changing concepts of evil and the demonic. It can be read as a lesson in exalted monotheistic theology, but it was and is used for magical purposes, including for exorcism and demon-fighting. As threats have evolved in various societies, so interpretations of Psalm 91 have developed to accommodate each new reality. The psalm's language about demons and evil forces has repeatedly come into play when Christianity encounters other religious traditions. At every stage, interpretations have to be understood in the larger context of social, spiritual, and practical concerns--indeed, a biography of Psalm 91 is also a history of critical themes in Western religion.