What is the meaning of the very last stanza of "The Raven"?

The
importance of the last stanza is made evident by the tense shift. The action changes from verbs
like "Swung," "tossed" and "shrieked" to "is sitting."
This decent into chaos for the poem's speaker has become something that is happening, not
happened. 

This tense shift makes the poem more frightening in that, up to
the last stanza, the entire narrative seemed something that had happened long before, perhaps
around the time the speaker lost his loved one named "." But when the speaker shifts
to present tense, it's clear that this personal chaos will not end. With this last stanza, Poe
makes sure the reader knows that this ongoing hopelessness is more frightening than a creepy
tale about a bird who seems supernatural.

In addition, the stanza includes
some intensethat suggests the speaker's life is chaos. The raven has "eyes all the seeming
of a demon's" and the light from outside casts an eerie "shadow on the floor."
Then the speaker compares himself to this shadow. He sees his "soul from out that shadow
that lies floating on the floor." 

Overall, Poe constructs the poem in a
way that the last stanza serves as a shock. He uses the tense shift and some intense imagery to
show that personal chaos is more frightening than a creepy story.