The speaker says that “the Soul selects her own Society—” and then “shuts the Door,” refusing to admit anyone else—even if “an Emperor be kneeling / Upon her mat—.” Indeed, the soul often chooses no more than a single person from “an ample nation” and then closes “the Valves of her attention” to the rest of the world.
This poem about friendship or of love, if you prefer, illustrates why Dickinson has been called the poet of exclusion. The poem describes choosing a friend (or lover), and rejecting (excluding) all others