"What if a demon crept after thee into thy loneliest loneline..." — Friedrich Nietzsche quote meaning

What if a demon crept after thee into thy loneliest loneliness some day or night, and said to thee: "This life, as thou livest it at present, and hast lived it, thou must live it once more, and also innumerable times; and there will be nothing new in it, but every pain and every joy and every thought and every sigh, and all the unspeakably small and great in thy life must come to thee again, and all in the same series and sequence—and similarly this spider and this moonlight among the trees, and similarly this moment, and I myself. The eternal sand-glass of existence will ever be turned once more, and thou with it, thou speck of dust!"—Wouldst thou not throw thyself down and gnash thy teeth, and curse the demon that so spake? Or hast thou once experienced a tremendous moment in which thou wouldst answer him: "Thou art a God, and never did I hear anything so divine!" If that thought acquired power over thee as thou art, it would transform thee, and perhaps crush thee; the question with regard to all and everything: "Dost thou want this once more, and also for innumerable times?" would lie as the heaviest burden upon thy activity! Or, how wouldst thou have to become favourably inclined to thyself and to life, so as to long for nothing more ardently than for this last eternal sanctioning and sealing?