Emily sets up a series of contrasts between the “I” and the “Her” (which could be Sue, or the Muses) in which the “Her” is “fit” for something that “I” cannot give. “I” lacks material riches and pedigree but can use the “twigs and twine” available to at least build an emotional relationship with “Her”.
There are some people who argue this poem is about her friend Sue while other people argue this poem is about poetry (the muses), but I don’t think it has to be an neither / or situation because both seem appropriate at the same time. Sue could very well be the must for this poem at least – perhaps many more.
The first line seem straightforward enough on first reading in that it Emily is glorifying the “breast” (the character) or this “Her” as being suited to wear expensive finery. However, the word “fit” is doing extra work here in that not only does she mean that these “pearls” “fit” on “Her” (as in they belong; is suited for) but a “fit” is also an obsolete term to describe a part of a poem or a song (OED) but the word was in use in Emily’s time. Thus Emily could also be saying that her poetry is fit for “pearls” just as Sue is.
The second line stands out because she puts the word “Diver” in quotes. The meaning of this line would not seem to be lost without the word in quotes, but I believe she’s using the word to also do double-duty. At first reading she is referring to the image of pearl divers and that she is unable to diver for pearls to give to “Her”, but a “Diver” also refers to a pickpocket (OED) so Emily could be implying that she isn’t someone who can pluck beautiful words / pearls from their home to “fit” into a poem. I’m not suggesting she alluding to thievery, but the word choice might be referring to how she might think about inspiration and where the right words / pearls come from in that she has to be like a pickpocket to find the perfect ones. In other words, she’s possibly alluding to a deftness and nimbleness to choosing the right words.
The third line is unusual in that Emily does not write that “Her brow is fit for” crowns, she says “thrones” instead. How can a “brow” be “fit” for a thrown when crowns are what sit on brows? I think the answer to this question is that because Emily is a talented poet she does not dive for the obvious word choice. Let’s say she had used the word crown – we would have the image of “Her” wearing a crown, perhaps one trimmed with “pearls” from the first line. Yet when Emily uses “thrones” she expands the image to paint a picture of a royal figure sitting on a thrown who is also wearing a crown. We imagine a queen and all her glory, but if Emily had just used the word “crown” we actually would have not imaged someone so glorious since we would have only been focused on her physical characteristics and not her entire persona as a queen. By being unexpected, she uses a word associated with a crown to enlarge the importance of “Her” and it creates a more detailed image in our imagination.
The fourth line build off the royal persona and majesty of the previous line by suggesting that Emily does not have the pedigree (“crest” as in family crest) to stand before the queen in her court. Not only is she not adept at finding “pearls”, she lacks the lineage to even stand in “Her” presence. And Emily could be referring to her situation as a woman writer in New England in the 19th century as someone who does not have the pedigree of someone like the famous poets of her time or the social standing to allow her to find her own way as a poet.
Yet in the next line, “Her heart is fit for rest” (though in other drafts the word “rest” is switched to “home”) she is saying that regardless of one’s pedigree, “Her” heart is willing to accept anyone to “rest” there. And there might be some subtle wordplay going on in this line too with not only the use of “fit” to refer to a section of poetry, but “for rest” could be read as forest, meaning the wilderness in which Emily lives as a poet outside of the cultivated lands of the poets who have the pedigree to stand before the queen, and it also sets up the image of the following lines in which a “sparrow” builds its “nest” in “Her heart”. In other words, “Her heart” is a part of a poem in which there is a wild place inside of it. And this could tie back to Emily’s feelings towards Sue in that Emily has a wild place in her heart for Sue, but Emily also wants to use the word “home” as a place away from the forest (the wild place) where she can be safe. Thus home and “rest” seem to be at odds with each other in points to a conflict within Emily’s own “heart” about her feeling towards Sue and towards poetry.
Thus the home that is built in the final three lines of the poem incorporates a wildness and the domestic. Emily compares herself to a “sparrow” and in the next line she might be referring to Sue as “sweet” (as in darling, beloved) and not just that Emily’s “nest” is made of “sweet” (pleasing) “twigs and twine”. And the use of the word “twine” seems to allude to the entire poem in that she not only referring to something string-like with which a bird uses to build a “nest”, but also to “a fold; a coil; a convolution; a twist or turn in the course of anything” (OED). The poem does feel coiled, as if it has multiple, interlocking pieces that when unraveled (like the fit of a poem) might seem convoluted, but when put together creates a unified whole; she’s taking something wild and making it domestic and she can do this all year round.
Emily might say that she is not a “Diver” but I believe she is well aware at just how adept she is plucking “pearls” from their oyster. She knows how to build a queen out of a throne and she knows how to “fit” a poem out of “twine” into a “nest”. In fact, this is Emily showing off how good she is.