Emily was an avid letter writer and this poem was part of a letter to her cousin Eudocia Flynt which included a rose, both an actual rose and this poem describing a rose. I think it’s a stretch to attach an overt sexual connotation to this poem (I mean you can, but that simplifies the poem too much). Rather, she is also describing how the parts of language can be used to multiple effects but also come up short of the real thing.
The first line has some subtle wordplay in that letters refers not only to writing a letter for the post, but also the act of writing an individual letter of a word, such as l-e-t-t-e-r-s. She then explains that all these “letters” that she “can write” are also, somehow, not right, that no matter how many she writes, they’ll never be the right letters to replace what she’s feeling or describing. I think of her use of the word “write” in the nautical sense of righting a ship and that no matter how many “letters” she rights, they always remain capsized, perhaps in the “Depths”.
There is also another definition to the word letter, and this was surprising when I looked it up, and that it is the obsolete noun definition meaning “A person who or (occasionally) a thing which hinders or impedes; a hinderer” (OED). Thus, buried in the history of the word “letters” is the act of these same “letters” getting in the way of the real thing. And since Emily included a real rose to go along with her description of a rose, then she understands how what she writes can never replace the real thing.
However, she doesn’t give up on language. In fact she’s quite in love with it, such as how the word “Syllables” does have a velvety sound to it with all those soft S sounds and luxurious L sounds being drawn out slowly over three dexterous syllables. No wonder some people have compared this poem to the act of cunnilingus, especially when we consider the “Depths of Ruby” and the “Lip” – it’s easy to attach a sexual connotation to this poem. However, she is also describing how beautiful and mysterious a rose is, and it’s interesting that she never once uses the word ‘rose’ because though she is aroused by this rose, it remains “Hid”. Rather she talks around the word ‘rose’ perhaps because, like a letter which impedes or hinders true meaning, to say the word rose would mean whomever is reading this letter would imagine their own rose and not the one Emily has in mind and which she is trying to describe in beautiful detail. In other words, to say the word ‘rose’ is to define it, but to talk around it, to describe its quality and its effect is to somehow get closer to the truth of this particular rose.
One final note about the implied sexuality of this poem. If we read, say, Keats and his Ode on a Grecian Urn, we don’t immediately assume he’s being sexual in describing that evocative shape, so why do we ascribe sexuality to Emily when she describes a rose? It seems unfair to only connect a woman’s writing to the body and only the man’s writing to the mind because that is playing into gender stereotypes. Granted, Emily may have been aware of the loaded sexual imagery of this poem (though it was given to her cousin, so there’s that), but to make that the main emphasis of the reading of this poem feels very unfair to all the other work Emily is doing in this poem and it reduces Emily to a single dimension when in fact the majority of her work reveals that she has more dimensions than a rose has petals. I’m not saying we can’t read the sexuality in this, but there is a lot more going on here than a single dimension.