Emily Dickinson's "I died for Beauty - but was scarce" is at first glance a "Stanza", however it borrows from the ballad form as well. Its place as a Stanza is secured by the isometric line lengths, although line lengths in a Stanza may be unequal as well, and by its ability to stand as a self contained entity. However, what Strand and Boland (The Making of a Poem: A Norton Anthology of Poetic Forms) refer to as "a suppressed narrative" tells a story with hidden levels, of two people whose similar actions in life have created a bond between them in death. This hidden narrative draws the stanza into the realm of the Ballad.
Like a traditional ballad, "I died for Beauty - " delivers its short story in four-line stanzas. Also borrowed from Ballad form is a first and third line in each stanza with four stresses in iambic tetrameter, followed by second and fourth lines with three stresses, or iambic trimeter. Typical of the Ballad, Dickinson's piece uses an "a-b-c-b" rhyme scheme. Also, its themes are among the favorite of balladeers, death and the supernatural. Although not necessarily a staple of the Ballad, Dickinson makes use of dashes instead of traditional punctuation, creating both a flow and additional rhythm.
So the question remains, "Why would Dickinson's piece be considered a Stanza and not a Ballad?" From a technical view, the piece could very well be called a Ballad. But Dickinson's story moves beyond the communal, folk story realm of the Ballad and becomes a macabre scene which speaks to our deeper fears and desires. It reminds us how every aspect of life, our identity, companionship, and even idealism will eventually end in death. Where the Ballad merely relays a story, perhaps the story behind "I died for Beauty - " is taken into waters too deep for the traditional balladeer.
The poem speaks of the futility of martyrdom, how life ended for a cause ultimately ends in both the martyr and the message being forgotten. In this poem two recently deceased souls exchange reasons for death. The narrator died for one ideal and the companion died for another, but the two ideals are related and for their similarity as well as the martyrdom, the companions share a kinsmanship.
In death, the two enjoyed their idealistic connection. In the parallel world outside their tombs it is possible both were remembered for their idealism and how they followed it to their graves. But in time the moss grew to cover up both their lips and their names, making the two of them both mute and forgotten. Although they had "talked between the rooms" for a time, and presumably enjoyed their unity in idealism for awhile, in time death brought an end to these things. In a similar way the message behind their deaths, along with even their names, were likely forgotten in time by the outside world.
It is possible Dickinson is referring to the idealism behind her own poetry. John Keats' "Ode to a Grecian Urn" had been written about 60 years before and Dickinson might be imagining herself buried next to Keats, who died before his poems became famous. If his idealism was for truth and hers for beauty, perhaps Dickinson believed both of them would be forgotten in time and their efforts would both have been futile.