Her falt'ring hand upon the balustrade, Old Angela was feeling for the stair, When Madeline, St. Agnes' charmed maid, Rose, like a mission'd spirit, unaware: With silver taper's light, and pious care, She turn'd and down the aged gossip led To a safe level matting. Now prepare, Young Porphyro, for gazing on that bed; She comes, she comes again, like ring-dove fray'd and fled.
Angela intercepts Madeline on her way to her room, and leads her down the stairs to her bedroom.
Again, Madeline is described in otherworldly language: she's "charmed," she's compared in a simile to a "spirit" on a mission—if you're looking for extras to play elves in The Lord of the Rings, Madeline's your girl.
For the second time (the first was in stanza 5), the poem's speaker directly addresses someone, although this time he speaks to Porphyro.
He (or she, we still can't tell as this point) tells Porphyro to get ready for the show—literally, get ready to "gaze"—and makes everything that's going on feel a lot more immediate, like it's unfolding just as we read.
The speaker announces the arrival of Madeline, whom in another simile he likens to a dove that's flying away from a predator.
This seems like a funny way to describe Madeline—so far, she's been off in her own world, but she hasn't been afraid. At the moment when Porphyro and Madeline are finally in the same space, though, she's described as a helpless animal that wants to avoid being some other animal's lunch.