In his book How to Read a Poem, Edward Hirsch writes that poetry has "a stored magic." This magic that poetry possesses derives from the multiple images, meanings, and lyricism that issue forth from words placed in unusual ways.
The order of words in poetry, just as in declarative sentences places emphasis often upon those words that begin the line or are paired with other words. For instance, in a poem written by Dylan Thomas, emphasis is placed upon the words that create alliteration in /f/ that moves the poetry at a rapid pace in the first stanza, giving the poem a sense of the transitory nature of time.
When all my five and country senses see,
The fingers will forget green thumbs and mark
How, through the halfmoon's vegetable eye,
Love in the frost is pared and wintered by....
The arrangement of the second line with "fingers" in the normal order of the subject of a sentence places the importance of the line's key idea upon this subject, "fingers" just as "Love" in the fourth line is the most important word/idea.
However, in his eighth line, Thomas breaks from the normal English sentence pattern of Subject + Predicate + rest of the sentence, and thereby places emphasis upon words that are not the subject of the sentence:
And, lashed to syllables, the lynx tongue cry
This inverted word order establishes a ranking of ideas, thus giving the metaphoric phrase "lashed to syllables" more emphasis than the subject "tongue." Further, the altering of word order often lends figurative meaning to words which would normally not have this. In a rather poor example, "a sound sleep" differs in meaning from "a sleep sound." And, certainly, the arrangement of the order of words affects the rhythm of a poem. Placing words within a line in a planned order can, for instance, create internal rhyme, while placing them at the end of a line can affect the rhyme scheme. This use of rhyme, of course, is mainly a sound device; however, at times rhyme can alter meaning as it can create a humorous or emotional effect that differs from a line without such rhyme.
Poetry can be like a recipe. If you were making a cake, you would first mix the dry ingredients together; then you would cream butter and sugar together, then add eggs, then stir the dry ingredients in. Why wouldn't you just drop all of the ingredients into a big bowl at the same time and mix? You'd end up with a lumpy mess, and no one wants a cake, or a poem, to be a lumpy mess. Word order matters—sometimes for clarity of meaning (a solo guitar isn't the same as a guitar solo) and sometimes for effect ("a dying man" is roughly the same as "a man, dying," but the effect of the word order matters). There are many different ways to order words and communicate approximately the same meaning, so readers should always question why poets have chosen a particular order, whether the choice is conventional or just the opposite.