Writers and poets use figures of speech (also referred to as “figurative language”) to make comparisons that convey meaning to their readers. Generally speaking, a figure of speech is a statement that is not literally true; it is “figuratively” true in the sense that it conveys important information. Some common figures of speech are similes, metaphors, symbolism, and personification.
William Wordsworth uses several figures of speech in the poem “She Dwelt Among the Untrodden Ways.” This poem is an elegy (a written or spoken tribute to a deceased person) for a woman named Lucy. It is short, a mere 12 lines, so Wordsworth doesn't tell us much about Lucy. He wants to make us understand that Lucy was beautiful in a unique way, and also that she lived in an out-of-the-way place and did not know many people. He does that in the poem's second stanza, first with this metaphor:
A violet by the mossy stone,
Half hidden from the eye
This metaphor compares Lucy to a violet. The metaphor is appropriate for Wordsworth's intention for several reasons. A violet is a particularly beautiful flower, so the metaphor reflects the speakers opinion of Lucy's beauty. Notice that he doesn't just call her a violet, but he also says that the violet was half-hidden by a mossy stone. Lucy lived in the country and, like this violet, was easy to miss.
The metaphor is immediately followed by this simile:
Fair as a star when only one
is shining in the sky.
Here the speaker again characterizes Lucy as beautiful, this time by comparing her to a star. But this time he emphasizes her uniqueness—she is one of a kind. He asks us to consider how beautiful a star would be if it was the only one in the sky. Like such a solitary star, Lucy is a unique beauty. Perhaps he means that she is the only beauty in that place, or perhaps he means she is beautiful in an unusual way—he doesn't say.
Figures of speech allow writers and poets to express meaning in a memorable, sometimes surprising way. Since we know first hand what a violet and a star are like, the comparisons give us a deeper understanding of Lucy than a simple explanation could.