"La Belle Dame sans Merci" is a popular form given an artistic sheen by the Romantic poets. Keats uses a stanza of three iambic tetrameter lines with the fourth dimetric line which makes the stanza seem a self-contained unit, giving the ballad a deliberate and slow movement, and is pleasing to the ear. Keats uses a number of the stylistic characteristics of the ballad, such as simplicity of language, repetition, and absence of details; like some of the old ballads, it deals with the supernatural. Keats's economical manner of telling a story in "La Belle Dame sans Merci" is the direct opposite of his lavish manner in "The Eve of St. Agnes". Part of the fascination exerted by the poem comes from Keats' use of understatement.It is a love story.
Keats sets his simple story of love and death in a bleak wintry landscape that is appropriate to it: "The sedge has wither'd from the lake / And no birds sing!" The repetition of these two lines, with minor variations, as the concluding lines of the poem emphasizes the fate of the unfortunate knight and neatly encloses the poem in a frame by bringing it back to its beginning. Keats relates the condition of the trees and surroundings with condition of the knight who is also broken.
In keeping with the ballad tradition, Keats does not identify his questioner, or the knight, or the destructively beautiful lady. What Keats does not include in his poem contributes as much to it in arousing the reader's imagination as what he puts into it. La belle dame sans merci, the beautiful lady without pity, is a femme fatale, a Circe-like figure who attracts lovers only to destroy them by her supernatural powers. She destroys because it is her nature to destroy. Keats could have found patterns for his "faery's child" in folk mythology, classical literature, Renaissance poetry, or the medieval ballad. With a few skillful touches, he creates a woman who is at once beautiful, erotically attractive, fascinating, and deadly.
Some readers see the poem as Keats' personal rebellion against the pains of love. In his letters and in some of his poems, he reveals that he did experience the pains, as well as the pleasures, of love and that he resented the pains, particularly the loss of freedom that came with falling in love. However, the ballad is a very objective form, and it may be best to read "La Belle Dame sans Merci" as pure story and no more.