When analyzing a poem, it is best to identify the controlling metaphor. Often the title is a clue, as it is with Poe's poem, "The Spirits of the Dead." For, these words seem to be the key to understanding the poem:
Be silent in that solitude,
Which is not loneliness—for then
The spirits of the dead who stood
In life before thee are again
In death around thee—
The spirits of the dead will come to the speaker and surround him and he will be able to communicate with his beloved. The "mystery of mysteries," the communication of the dead with the living, is made possible by his solitude which is a metaphor for the opening of the speaker's soul, a conduit that allows the "mist" to come in, which is a metaphor for the voice of the beloved. Thus, the meaning of the last stanza echoes that of the first as "the breadth of God" is the breeze which carries the message of the dead.
Perhaps, a good thesis statement could be the expression of the main idea of the poem. That is, the poet must allow himself solitude in order to sense the spirits of the deceased, who will communicate with those who are receptive.
As one critic writes, Poe believed that
[T]he task of poetry, then, is to induce a state of mind in the reader corresponding to the exaltation felt by the soul as it explores the limits of perception in search of ideal beauty.