One character quotes from the writings of 18th century Christian mystic Emanuel Swedenborg. Matheson bases his descriptions of the death experience itself on studies by Elisabeth Kübler-Ross and Raymond Moody. When reading these accounts, Matheson found that revived suicides told a far more frightening story than anyone else who had near death experiences. Matheson's bibliography consists more of "New Age" material than mainstream religious sources, and the novel shows reincarnation as more voluntary than major world religions like Hinduism, Buddhism, and Judaism usually depict it.