A great little post by Anthony Sacramone over at First Things about Law vs Gospel in Black Swan”, ht MS:

Nina [the ballerina, played by Natalie Portman] is simply too naive, too fragile, too “good,” even, to access the “dark side.” She is offering up only half a performance. She must “free” herself! Only then will she be capable of delivering the “whole,” even if it means a terrifying fragmentation of her personality.

But with a little help from her friends, and her own internal pressures, she gets better (or worse, depending on how you look at it). And better. Until she achieves that unity of purpose that renders the “perfect” artistic performance—to her ultimate peril.
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The film is not subtle and Nina’s inner life, her delusions and paranoid fantasies, trace the borderline of camp. But what is really missing is a way out of this false dilemma between “perfection” and “failure.” Perfection is in the eye of the beholder, and so in order to achieve it one must always subordinate the self to some other authority, which, in this realm, is always, always fallible. It is a self-defeating exercise, because even if you think you’ve achieved it, give it a minute, and the criteria by which that perfection is judged will shift, and you’ll find yourself having to place catch-up. To be perfect is, by definition, to fail. And the ultimate failure is death.

Which is why we Lutherans have placed such emphasis on law/Gospel dichotomies. Every time gospel implies “You must” or “You must not,” it becomes a word of condemnation, of failure, because, with all do apologies to Yoda, “you can’t,” try as you might. The good news is that someone already did, and you can rest in his success as if it were your own. You can put yourself under his authority without fear of collapsing under its weight, because his yoke is easy and his burden is light. The price of admission to perfection is faith alone, because the cost of that admission was paid 2,000 years ago. And faith is never a work. Only believe.

But Nina never hears that word, drowned out as it is by the disparate and competing demands of “You must.”