The Eve of St. Agnes is significant (although an often overlooked Keats poem) in the timeline of Keats's short life. It was written in 1819, which is the same year that he proposed to Fanny Brawne, and directly following the death of his brother Thomas. So it makes sense that love in its various forms would weigh heavily on Keats's mind at this moment in his writing career.
The two main characters in The Eve of St. Agnes, Madeline and Porphyro, are passionately in love, although their types of love differ initially. (Hers is more innocent; his is more passionate.) Unfortunately, Porphyro and his family have been cursed by Madeline's family, so this isn't exactly an accepted or welcome union. Through this, the reader sees the sometimes rigid societal expectations regarding whom one is supposed to love. Porphyro develops a plan through the help of Angela to sneak into Madeline's chamber and hide, where he watches "Her rich attire [creep] rustling to her knees." We see Porphyro waiting for the perfect moment to wake his beloved, content to let his love sleep while he "listened to her breathing, if it chanced / To wake into a slumberous tenderness." For several stanzas, Porphyro takes in this scene with full sensory details, from the "blanched linen" to the "manna and dates, in argosy transferr'd / From Fez." Porphyro understands the importance of this moment; ultimately he wishes to escape with Madeline so that they can love each other freely. After finally waking Madeline, they do escape together, leaving images of destruction in their wake.
Madeline's character captures many stereotypical expectations of women in love. She has angelic qualities: "She knelt for Heaven's grace and boon; / Rose-bloom fell on her hands, together prest, / And on her silver cross soft amethyst, / And on her hair a glory, like a saint; / She seem'd a splendid angel." Madeline possesses the rigid societal qualities expected in women: innocence, adoration of her beloved, and impeccable moral character.
Porphyro, on the other hand, is seen to embody society's expectations for men in love: passion, lust, and tendencies toward impulsive behavior. He comes to steal away his beloved and is even portrayed as ultimately her rescuer. Images of the stereotypical damsel in distress and women in need of rescue are seen especially in the beginning and ending stanzas.
The Eve of St. Agnes is written in Spenserian stanzas. Even at the time, this form was an older one to choose, adding to the romantic tone that it creates. This also allows for Keats to proceed through the action slowly, allowing the reader to soak up the details along with Porphyro instead of moving quickly to the climax and end goal: their escape. The reader feels a building sense of urgency that stems from this passion, as each moment is carefully crafted through sensory details within the Spenserian form.