This poem is significant because of its focus on a simple, obscure young woman. Though this may seem odd to us now, at the time Wordsworth composed these verses, it was unusual to write poetry—especially complimentary poetry—about common people. (An exception is Gray's earlier poem, "Elegy Written in a Country Churchyard," and Wordsworth, in his poem, echoes Gray's theme of simple people dying unknown and unseen.) Wordsworth's focus is on elevating and celebrating the worth of lower-class individuals, which he felt called to do (he explains this later in his autobiographical poem The Prelude).
Although the poem is short and uses simple words, Wordsworth is able to convey deep emotion through the quietude of the speaker's grief. The simple strokes outlining Lucy's life, depicting her as a person who had "none to praise" and who "very few" loved, adds to the poignancy of her death. The lack of detail gives her a universal quality: we can all probably think of someone who is completely unknown but whose life made a difference to the few she did touch.
Further, the speaker conveys his deep feelings through the use of exclamation marks, such as in the lines
A violet by a mossy stone
Half hidden from the eye!
—such as comparing Lucy to a violet—conveys her gentleness, and the nature imagery—comparing her to a flower and star—conveys a sense of both her beauty and her purity.
Finally, by the end of the poem, we sense that the poem is brief because the speaker cannot find adequate words for his grief. His silence is eloquent, as is his final, heartfelt couplet
But she is in her grave, and, oh,
The difference to me!