Nietzsche's infamous work Thus Spake Zarathustra is filled with a strange sense of religiosity that seems to run counter to the philosopher's usual polemics against religious faith. For some scholars, this book marks little but a mental decline in the great philosopher; for C. G. Jung, Zarathustra was an invaluable demonstration of the unconscious at work, one that illuminated both Nietzsche's psychology and spirituality and that of the modern world in general. The original two-volume edition of Jung's lively seminar on Nietzsche's Zarathustra has been an important...