Hume writes that the book evidently has a deeper meaning, which may be strictly allegorical or more broadly "visionary" like the work of William Blake; and that this has both attracted a cult following, and prevented the book from reaching a wider audience. Hume describes the planet of Arcturus, far from being a standard science fiction setting, as having a threefold function: the literal setting for a "quest romance"; the psychological frame, "a projection of the faculties of the mind"; and an allegorical paysage moralisé, like the moralised landscapes of Pilgrim's Progress or Piers Plowman.
