Enantiodromia

While I found Jung's theory of enantiodromia -- the conversion of things into their opposite -- equal parts vague and simplistic, there's no question that the way apparent opposites share a secret root is an idea dear to Nietzsche's heart.  It's expressed in many images throughout TSZ, and is stated as an explicit theory as early as the second aphorism of BGE.  But, as with most of his important ideas, Nietzsche doesn't just state this as a theory, but actually shows it to us in action by applying it to his own ideas.  The second point is more subtle and profound version of the first that requires careful reading to see.  For example, the following aphorism is situated in the middle fo the third chapter of BGE, where Nietzsche discusses "The Religious Disposition", or "The essence of religion", or, "What is religious", depending on your preferred translation.  

Anyone who has struggled for a long time, as I have, with a mysterious desire to think down to the depths of pessimism and redeem it from the half-Christian, half-German narrowness and simplicity with which it has most recently been portrayed, namely in the form of Schopenhauerian philosophy; anyone who has truly looked with an Asiatic and super-Asiatic eye into-and under­ neath-the most world - denying of all possible ways of thinking (beyond good and evil and no longer helplessly deluded, like Buddha and Schopenhauer, by morality) - this person may, without really intending it, have opened his eyes to the opposite ideal: to the ideal of the most audacious, lively, and world-affirming human being, one who has learned not only to accept and bear that which has been and is, but who also wants to have it over again, just as it was and is, throughout all eternity, calling out insatiably da capo, not only to himself, but to the whole drama, the whole spectacle, and not only to a spectacle, but ultimately to the one who has need of just this spectacle - and makes it necessary, because he continually has need of himself - and makes himself necessary.­
Well? And wouldn't this then be - circulus vitiosus deus? (BGE, #56)

Nietzsche is of course alluding here, for the first time in BGE, to the doctrine of eternal return.  Look carefully at how this crowning idea is presented though.  Not only is it presented in the context of a chapter that discusses the way religious sentiment ultimately stems from weakness, from a simple need to make the suffering stop, but Nietzsche directly traces the inception of his idea to following the Schopenhauerian or Buddhist view of the life as suffering all the way to its end.  In other words, ER is an explicitly religious doctrine.  Nietzsche is concerned with exactly the same problem that he claims has led to every religious solution -- what do we do about the fact that the world sucks?  Christianity "solved" this problem by inventing another world that doesn't suck, thus converting our world into a mere appearance, a test, a brief weigh station on the highway to heaven.  Buddhism is at least more honest about the problem itself, making it the first noble truth.  But Nietzsche interprets the Buddhist "solution" as another version of Shopenhauer's nihilism -- this world sucks and there's no other world that doesn't suck; the only escape from suffering is just to stop existing, to stop being reborn into the suck.  It's not important here whether this is a good interpretation of either Schopenhauer or "Buddhism" (and which Buddhism).  The point is simply to notice that these highest religious values -- heaven, the cessation of Nirvana -- are structured as the-opposite-of-suffering.

I think it's safe to infer from Nietzsche's biography that he was a man who knew a thing or two about suffering.  And he had a simple theory about how these religious doctrines came into existence.  They represented the creative genius of people who suffered a lot.  These poor weak people who suffered so mercilessly created a way for their suffering to end by creating a way for their suffering to mean something.  This is the upshot of Nietzsche's description of the fascination exerted by saints.

Until now, the most powerful people have continued to bow down with respect before the saint, as a riddle of self-discipline and deliberate, ultimate renunciation: why have they bowed down? Behind the question mark of the saint's fragile and pitiable appearance, they sensed the superior force that wished to test itself through a discipline such as his. It was the strength of the will; in it they recognized anew and were able to honour their own strength and lordly pleasure: they were honouring something in themselves when they honoured the saint. The sight of the saint also planted a suspicion in them: 'Such a monstrous denial, so contrary to nature, cannot have been desired for nothing,' they said to them­ selves and wondered. 'Maybe there is a reason for it, maybe there is some very great danger, which the ascetic, thanks to his secret counsellors and visitors, knows more about?' Suffice it to say, in his presence the powerful of the world learned a new fear; they sensed a new power, a strange enemy, still unconquered: it was the 'will to power' which brought them to a stop before the saint. They needed to ask him -- (BGE, #51)

The saint overcomes his suffering by means of his religious belief.  The denial and denigration of life he counsels is actually the product of an extraordinarily powerful life within him.  Because for Nietzsche, there is no life beyond life, which is to say that there is nothing but the will to power, we see that the essence of religion is for the weakest life to save itself by slandering itself.  

The doctrine of eternal return is invented for the same reason as any religious doctrine.  It is designed to redeem the insupportable suffering of life by making it mean something.  It is inspired by the same pessimism about life taken to its nihilistic extreme.  But at this extreme point, it somehow converts into the opposite.  Instead of hoping for an end to suffering, an escape from the wheel of samsara, ER affirms this suffering into infinity.  Instead of wanting something to be different, ER wants it all to be exactly the same, forever and ever, amen.  Suffering isn't to be rejected and avoided, but embraced as such, to be desired again and again, as suffering.  Here, suffering transforms into joy without anything changing; the two were only apparently opposites.  The whole sordid spectacle of life is necessary in its entirety not because of some divine plan that governs it from without, but because it leads to the creation of a soul within it capable of needing it to be exactly as it is.  Nietzsche overcomes his suffering and himself with ER only by becoming exactly who he is -- the precise saint capable of inventing this new religion of affirmation, the one who is capable of it only because he stands in the direst need for it.  The purpose of suffering is to produce someone capable of giving purpose to suffering.  It's not clear whether this god should be called vicious or virtuous, but it's certainly a circle.