What does the third stanza tell the readers about Annabel Lee's position in society?

The third stanza provides the following crucial information: the young Annabel Lee was of a higher social class that the speaker. When her family gets wind of the fact that Annabel Lee is in love with the speaker, they are unhappy. They are not going to let Annabel Lee marry beneath her social station. Therefore, they arrive and take her away from the speaker, separating the two lovers:

So that her highborn kinsmen came
And bore her away from me

As a result, Annabel dies of a broken heart.
The romantic love between the two young people is thus pitted against the practical concerns of the older family members, who do not want their kin involved with someone who—in their eyes—is the wrong kind of person. The poem, told from the speaker's point of view, comes down strongly on the side of romantic love.
The speaker, who spends his nights by Annabel's grave, believes that not even death can truly separate him from his beloved Annabel Lee:


And neither the angels in Heaven above
Nor the demons down under the sea
Can ever dissever my soul from the soul
Of the beautiful Annabel Lee

Edgar Allan Poe's well-known poem "Annabel Lee" describes the speaker's love for the titular woman, who is now deceased. In the third stanza, the speaker says,

And this was the reason that, long ago,
In this kingdom by the sea,
A wind blew out of a cloud, chilling
My beautiful Annabel Lee;
So that her highborn kinsmen came
And bore her away from me,
To shut her up in a sepulchre
In this kingdom by the sea.

This stanza tells us that Annabel Lee is a member of the upper-class of society. The key phrase here is "highborn kinsmen." The word "highborn" means they are wealthy and of the upper class. They are "kinsmen," so they are Annabel Lee's relatives. This indicates that she is also "highborn." In the stanza, the speaker resents the actions of the kinsmen because they take her from him and "shut her up in a sepulchre," or a grave.

The speaker next describes Annabel Lee's tragic death before returning to more detail about his and Annabel Lee's relationships. The speaker says these "highborn kinsmen" cannot separate him from his beloved. He and Annabel Lee will always be together in spirit. He says, "our love it was stronger by far than the love / Of those who were older than we." He feels she is always with him, and he feels her eyes watching over him. The speaker describes himself lying next to his beloved's grave in a morbid scene that ends the poem and emphasizes how Annabel Lee will forever be in this tomb surrounded by the sea.