Joni Mitchell: "You could write a song about some kind of emotional problem you are having, but it would not be a good song, in my eyes, until it went through a period of sensitivity to a moment of clarity. Without that moment of clarity to contribute to the song, it's just complaining."
And that is every bit as true for a poem or, for that matter, any artistic work. I sometimes see discussions about the role of expression versus craft but I truly think that misses the point. Ms Mitchell gets it though; its about understanding. It's about having something worth saying. It is, indeed, about clarity.
Writing a poem is a search for clarity. Working with the structure of language allows one to find the connections and ideas that lie within words, to build a road of metaphor that leads to...well, somewhere we weren't before. To discovery. To understanding. And perhaps to new questions! After all, what good is a work of art that doesn't make one think at least a little bit? ;)