We wouldn’t need the word “prose” if it weren’t for poetry.
One must have a mind of winter.
The greatest lines in poetry are infinitely quotable while having no definite meaning. What is a mind of winter, and why must one have one? It doesn’t matter. Wallace Stevens’ greatness lay in his ability to produce these kinds of anti-aphorisms, seemingly wise but ultimately ungraspable: Thought is false happiness. She sang beyond the genius of the sea. The only emperor is the emperor of ice cream. And, most pointedly: The poem must resist the intelligence / almost successfully. (Or, nay, successfully!)
I believe that to read poetry, one must have a mind of poetry. You must enter a state where you come to understand meaning-resistant arrangements of language as having their own kind of meaning. It’s quite similar to those Magic Eye posters from the ‘90s: If you haven’t figured out how to look at them, you can’t believe that anyone really sees the dolphin. (This metaphor has its limits, making learned skill seem like an on/off conversion; too, with poetry, even when you’ve mastered “the trick,” not everyone sees the same thing.)
Is this “negative capability”? I’m not sure.
Negative capability, as described by Keats, is rather delightfully poetic in itself, a form of imitative fallacy in criticism, a mental onomatopoeia. It seems clear enough by his own definition: “when a man is capable of being in uncertainties, mysteries, doubts, without any irritable reaching after fact and reason.” But it’s so often badly paraphrased, in conversation and in print; Wikipedia defines it as “the capacity of human beings to transcend and revise their contexts” (to their credit this merits a “citation needed”). A concept so frequently muddled must be inherently mysterious and as such, perhaps, a shibboleth; if you don’t understand negative capability you won’t understand poetry.