The narrator of the poem is reflecting on her death and how going home is a mistake. She goes to the house she used to frequent so much, only to find her friends having a feast and laughing happily. They are concerned for what tomorrow holds for them. The narrator becomes sad and realizes her friends are not mourning her death.
"To-morrow," said they, strong with hope, And dwelt upon the pleasant way: "To-morrow," cried they once and all, while no one spoke of yesterday. Their life stood full at blessed noon; I, only I, had passed away: "To-morrow and today," they cried; I was of yesterday."
The poem shows how difficult it would be, to return and see everyone you cared about having fun and not remembering you or your passing. All of her friends are full of life and their plans for the future, all the while, the narrator is sad because no one is mourning her passing. This poem goes on to show us our real fears. Don't we all want to be remembered? The narrator realizes that she is forgotten, like yesterday.
Rossetti's narrator utilizes imagery and language connected to life and death to express her sense of regret and sadness about having passed on.
Her friends remain alive, "jest[ing]" and "laugh[ing]" in the first stanza, while "beneath green orange boughs; ... they pushed the wine ... They sucked the pulp of plum and peach". All of this nature imagery strongly reinforces the fact that her friends are alive and the narrator is not, as the trees are full of leaves and the plums and peaches are growing healthily and being feasted upon.
In the second stanza, the repetition of "tomorrow" again calls attention to the death of the narrator, because for her there is not "tomorrow", only death. Her friends describe all the journeys they plan to go on, which the narrator cannot because she has passed on. Even when one friend says, "To-morrow shall be like / To-day, but much more sweet", the narrator cannot empathize with the friend's perspective because in death, all of her days are the same. In the third stanza, the narrator describes herself as "of yesterday", divorced from the past that "tomorrow" promises.
The final stanza again reinforces the narrator's sadness, because she is "all-forgotten" and has become a "guest" in her own home. Her friends do not seem to honor her memory, and she has become divorced from the life she once lived. Because she is a "guest", she cannot (or does not feel) she can stay long in the place that was once her home. Her loneliness comes to an apex at the end of the poem, as she describes herself as a guest who "tarrieth but a day" - someone who can only stay for a little while.