The speaker is somebody who seriously believes in the power of poetry. How do we know? Well, she wrote a whole poem about it, so we feel like it's a safe assumption. We mean, c'mon, she opens the poem with these two lines:
I dwell in Possibility –
A fairer House than Prose – (1-2)
So, according to the speaker, poetry is sweet, and prose is not so sweet because it's way more limiting than poetry. The speaker is a person who really values the power of poetry to expand the human mind—to push us into thinking about the infinite Universe around us. She's so hardcore about this that she doesn't even use the word poetry; she simply calls it "Possibility."
Poet Is as Poet Does
The speaker also makes it reasonably clear that she is actually a poet herself and not just a poetry fan. Check out these lines:
Of Visitors – the fairest –
For Occupation – This – (9-10)
When she uses the word "Occupation," she signals that this is what she does all day—must be nice. And when she refers to "Visitors," she makes us think she's talking about outsiders who are coming to check out her work (a.k.a. readers).
So our speaker is a super dedicated poet, one who might even be so dedicated to poetry that she'd hide away in a house and write for her entire life. The whole poem is one big extended house metaphor, right? We wonder if it's a house in… oh say, Amherst, Massachusetts? Okay okay, we'll stop. We know it's wrong to assume that the speaker is the poet, unless we're explicitly told so.
But even if the speaker isn't exactly Ms. Dickinson, herself, they sure do share a lot of similarities.