Here is the short BGE 37:
"Wie? Heisst das nicht, populär geredet: Gott ist widerlegt, der Teufel aber nicht -?" Im Gegentheil! Im Gegentheil, meine Freunde! Und, zum Teufel auch, wer zwingt euch, populär zu reden! -
Roughly: "'How is that? Does that not mean, to use a popular idiom: God is refuted, but the devil is not?' On the contrary! On the contrary, my friends! And who the devil is forcing you to use popular idioms!"
BGE 37 follows on the notorious argument in BGE 36, the conditional "proof" of the doctrine of will to power, one that involves premises Nietzsche plainly rejects. 36 concludes with the claim that the world is "just this 'will to power' and nothing else." Hence the start of 37, which basically means, "Are you serious, so what does this mean?" And one interpretation, the one Nietzsche wants to reject, is that if the world is will to power, then that means the world is not governed by a benevolent God but is instead hostage to the malevolence of the Devil. But, and this is Nietzsche's point, this misunderstands the nature of the "doctrine" of will to power: will to power is neither benevolent, nor malevolent. Insofar as things are "simply" will to power they are without any normative significance: they just are. So the popular idioms misunderstand the thesis from BGE 36.
This, of course, is consistent with a recurring theme in Nietzsche and in BGE, namely, that what happens is "beyond good and evil," that is, beyond assessment in terms of what ought or ought not to happen. There is no space for "ought," there just is what happens.
UPDATE: Dinner and family obligations led to a somewhat rushed conclusion to yesterday's post, and prevented me from addressing some additional, related sections of BGE.
But first, to return to BGE 37: bear in mind that on the Clark-inspired reading of BGE 36, N. does not really believe that the world is "'will to power' and nothing else." So why, then, is it important for him to disabuse the reader of the idea that if the world were will to power and nothing else, this would have no normative implications?
The immediately following section, BGE 38, talks about the various reactions to the French Revolution, introducing the important idea "that the text has finally disappeared under the interpretation [Interpretation]." The "text" in this context represents the actual event, the "interpretation" an evaluatively interested rendering and distortion of the actual event. In BGE 22, we encountered the first suggestion that someone "with an opposite intention and mode of interpretation" might read the text of the world not as exemplifying "conformity to law" but as exemplifying " a tyrannically ruthless and pitiless execution of power claims." But "this is interpretation, not text" in both cases. (BGE 22 ends with the famous, or infamous, concession by Nietzsche that if this doctrine of will to power "is only an interpretation...well then, so much the better.") So BGE 22 lends support to the Clark-inspired reading of BGE 36: in both cases, the doctrine of will to power is an interpretation, but not a case of "the art of reading well," of "being able to read facts without falsifying them through interpretation" (A 52). What BGE 37 then does is clarify that this particular "interpretation" is not meant to vindicate either God or the Devil: whatever the intention underlying this interpretation, it is not an intention to show that the world is really benevolently organized or malevolently organized. What then is Nietzsche's intention, what evaluative aim motivates this interpretation? We might say, borrowing a later phrase from Twilight of the Idols, that the intention of this interpretation is to illustrate the "innocence of becoming," of all that happens--the moral innocence, that is.
We have to be careful here, though, since I take it Nietzsche does think that the text of becoming really is innocent. Of course, Nietzsche can believe that without believing that the explanation for its being innocent is the "doctrine of the will to power." Rather, the "doctrine of the will to power" is an interpretation of the text that can be used to highlight or emphasize the innocence of becoming, at least as long as a reader doesn't make the mistake he wants to guard against in BGE 37.