The title promises that this poem will be a "portrait of a woman," and straight off the bat the speaker seems to announce who this woman is: "You are..." But even if line seems to be grammatically straightforward, it's hard to figure out exactly what the speaker means. First of all, why is the "you" separated from "your mind?" How can a person and her mind be two separate entities? Second, who is included in "our?" Is the speaker actually more than one person, or does he represent of a larger group? What kind of people are in this group?
Great minds have sought you – lacking someone else. You have been second always. (6-7)
Wow, that's really nice. The speaker is basically saying, "OK, lady, you're the default, the backup plan." But we don't know to whom she is second. What would be the first choice for these "great minds?" Exactly what are they looking for? Great hair? A good squash player? A spelling bee champion? Our guess is that the speaker means that these "great minds" seek out a muse (just as the "femme" here is the muse to this poem) – so the woman is being judged based on her ability to inspire.
You preferred it to the usual thing: One dull man, dulling and uxorious, One average mind – with one thought less, each year. (8-10)
This is the one moment we can find in the poem in which the speaker seems to reference traditional gender roles. (You might be able to find more!) The speaker indicates here that the woman prefers all these "great minds" (men) coming and going – even if she is their second choice – to being stuck with one really boring guy. A hundred years ago, when this poem was written, marriage was the obvious "career choice" for most women. The speaker suggests here that the woman is defying that convention.
You are a person of some interest, one comes to you And takes strange gain away: (14-15)
Again we have the "you are..." format, and again we're left unsure of what the speaker really means. Check out the vagueness is here, with phrases like "some interest" and "strange gain." What kind of interest? How much interest? What about this "gain" makes it strange?
No! there is nothing! In the whole and all, Nothing that's quite your own. Yet this is you. (28-30)
The speaker is a master at making us think he is telling us something very clearly but leaving us totally confused. So here is a 30-line poem, filled with references to London, the Sargasso Sea, ships, furniture, and oceanic debris, which the speaker claims will produce a picture of a woman. We read through all these lines and try to piece them together to figure out who this woman is, only for the speaker to announce at the very end that, actually, nothing really belongs to her, and that this nothingness is her. What? You might notice that the last line is indented. Could this mean that the "this" (of "this is you") refers back to the entire poem (everything said in the last 29 lines), rather than just the "nothing" of the previous line?