In stanza 1, when Death, personified as a "kindly" man, stops for the speaker and takes her away in his carriage, she notes that Immortality also sits inside it with her. Other than being mentioned as a fellow traveler, however, this figure remains abstract and undescribed, reflecting the speaker's unfamiliarity with Immortality as the journey begins.
The presence of Immortality as a figure tells us from the start that death is not an end, but a new plane of existence in the speaker's experience. She has died, but she has, paradoxically, moved to a place where she is immortal and cannot die again. Here, time moves very slowly, with "Centuries" seeming shorter than a day. Immortality's presence with the speaker suggests that he is there to help shepherd her to her new, at first inexplicable, existence.
In contrast to death usually being depicted as frightening, the humanized figure of Death in this poem is familiar and domestic, almost comforting. He, too, acts as a companion to the speaker.
Dickinson's personification of Death and Immortality connect the poem to medieval morality plays, in which abstract concepts, such as virtues and vices, are given concrete form. Dickinson does her best in this poem to concretize death, and the speaker's two companions speak to that strategy.