This poem is not usually conceived of as a riddle, but rather as a description of those instinctive preferences and choices, those defiantly nonrational elections and allegiances, like love, that we all make, without regard to personal advantage, to rank or to estate. To the degree that the poem has been construed as a private and guarded revelation of the poet's emotional life, and to some circumstantial events in it, there is a dispute about whether the choice of "one" means someone else or the poet herself; whether she is electing the solitude of a society of one, or committing herself to another. And it is not out of place, I think, to construe the poem as being about love. The mixed metaphor of the last two lines ("Then close the valves of her attention/Like stone") could be rather comfortably resolved if we substituted "heart" for "soul," since hearts can be "stony" and they have valves.
But I suggest that the power of this poem derives from a suppressed riddle, an unstated but implied parallel. As the soul is to its society (absolute, arbitrary, ruthless) so is God in His election and salvation of souls. Moreover, it seems to me that the second stanza not improbably suggests the adoration of the Magi, though I have no care to press that point. Still, the ominous quality of the final words is considerably amplified when the ultimate mystery of election is taken into account. We play at being God; it is characteristically human of us to do so.
From "The Riddles of Emily Dickinson." Obbligati (Atheneum, 1986).