In light of my Dickinson post of the other day, I thought I'd add here a remarkable, useful passage from an essay by Heather McHugh called "What Dickinson Makes a Dash For," from her book BROKEN ENGLISH. I'm not sure anyone ever said this better.
"Eudora Welty says the writer's work is to detect the pattern beneath the given, a shape at once lyrical and mysterious and felt, which 'is the form of the work...underway as you write and as your read.' (Writer and reader both do it, intuit the shape in the act, and their acts are by no means opposed.) The mysteries of meaning (at-once-still-and-moving, at-once-part-and-whole, at-once-read-and-written) obtain in literary as in spiritual realms. They resist logical codification because they sense, inside all diction, contradiction.
It is not the definable (delimiitable) finally, that interests Dickinson; she is drawn precisely to that uneasier thing, what can't be said. The relative exhaustibility of a literary construction is one measure of its inadequacy to this truth; and Dickinson's sentences and lines often seem designed (in judicious ellipses, elisions, contractions, puns and dashes) to afford the greatest number of simultaneous and yet mutually resistant readings. Where a lesser writer might try to comprehend the world by adding more and more words to his portrait of it, Dickinson allows for it, by framing in opposites or absents, directing us to what is irresoluble or unsaid, Where the addition of a word would subtract even one of the cohabitant readings in a text, she leaves the sense unsteady and the word unadded, What critics sometimes lament as cryptic or obscure in her work proceeds, I think from this characteristic reticence - a luxurious reticence, a reticence which sprouts and branches meaning in many directions, the way more exhaustive (less ambiguous) texts cannnot... Her richest work is precisely what critics since Higginson have called 'elusive,' and its signature is the sign of the dash -- that suspense of punctuation, that undecidabiity, which is not an indecision."