Of course, my background is science, not art, so my thoughts on this have even less credibility than my thoughts on (say) Intelligent Design. And this is probably a really trivial observation - GCSE standard or below - and I just was not paying attention in class when the teacher mentioned it as a throwaway remark.
However, it occurred to me that prose is about ideas, rather than format. So the precise words are less important than the ideas that are conveyed. Take a passage of prose, and it could be rewritten in different words, but conveying the same idea.
Poetry is different. Certainly it will convey an idea, but the words themselves are important - with well-written poetry, every word is the "right" word; none can be changed without reducing the quality of the poetry.
This bears on (for example) the issue of translation. A passage of prose can be translated into a new language, because the words themselves are less important than the ideas conveyed. It can be rewritten for a different audience for the same reason - they may not share the same culture or presuppositions, but the idea can be represented in different language, perhaps with additional explanation. There are some things which don't translate so easily - figures of speech, for example, or ideas that are linked to a particular culture, or particular sections which follow more closely poetic patterns. But that highlights the general fact that "prose" translates, whereas "poetry" and "poetic language" don't translate so well.
A poem can't be translated in the same way as prose at all. There will be some things "lost in translation", because the nature of poemosity (poemness?) is that it is the actual words which are significant. Even when a poem can be converted into a poem in another language, there won't be a direct equivalence between the response to poetry in two different languages.
It would be interesting to explore this idea further, but my knowledge of poetry and prose and different languages is too limited. I think I'll have to do some linguistics. As an example of poetry, it would be interesting to see how similar "Ein' Feste Burg" is, in people's response, to the two different English translations, "A Safe Stronghold our God is still" and "A Mighty Fortress is our God." Though in that case, of course, the music also adds to the response obtained.
This also has a bearing on evolutionary theory, interestingly....
An idea can be expressed in different ways. Similar biological structures (different forms of eye, for example) have apparently evolved separately, and do the same thing using substantially different genetic material. Here are "prose" ideas expressed in different ways. The assumption of darwinism is that all biological structures are of this sort - a gradual process of improvement will allow a movement towards a state where the biological structure is more fit for purpose - where the prose more correctly expresses the ideas that it needs to express.
But by the same token, people argue against simple darwinism by suggesting that some biological structures are highly specified. Like a poem, any substantial changes (much more than at the level of changing the spelling of a word, for example) are likely to rapidly erode the quality of the structure. Prose can be bashed into shape - a plan worked out, ideas sketched, arguments for and against marshalled and then the masterpiece written. But poetry, it might be suggested, doesn't work like that. Certainly a plan for a poem can be come up with - but I guess the poet is likely to pick specific words and phrases from his or her vocabulary, to construct the whole poem in a sense "as a whole", rather than gradually converge towards the final form. Words might be replaced, or stanzas - whole verses dropped or added. There may well be structural rules (metre, rhyme) that mean that the "prose" approach of converging towards the final version with proofreading, editing and so on simply won't yield a poem.
Hum. This merits some more thought....