Get out the microscope, because we’re going through this poem line-by-line.
That ancient Beadsman heard the prelude soft;
And so it chanc'd, for many a door was wide,
From hurry to and fro. Soon, up aloft,
The silver, snarling trumpets 'gan to chide:
The level chambers, ready with their pride,
Were glowing to receive a thousand guests:
The carved angels, ever eager-eyed,
Star'd where upon their heads the cornice rests,
With hair blown back, and wings put cross-wise on their breasts.
- Suddenly, in addition to the music, we have some sense of movement (people hurrying around have left the doors open), and the feel of the poem changes somewhat.
- It sounds like these people are having quite the shindig ("A thousand guests"? Think of the bar bill.). There's so much coming and going that they can't keep the doors closed.
- We've got more music, here, but it's got a different feel this time: instead of the "golden tongue" of yester-stanza, we now have "silver, snarling trumpets" which are "chiding." The music, which was all inviting and soft just moments ago, is getting a lot more aggressive.
- Aaaand cue the lights.
- Like in the chapel, there are statues here, but instead of the cold, dead, praying ancestors of the chapel, these are much more lively, "ever eager-eyed" angels, staring down ("Star'd" here is a poetic way of writing "stared") and carved with their hair blown back.
- As you probably figured, the angels aren't actually staring and the music isn't actually "chiding" (teasing or correcting)—that's just Keats throwing down some handy-dandy anthropomorphism. While anthropomorphism generally just means "non-human things doing human stuff," here you specifically have artistic creations taking on human agency.
- Let's find out if more of this is going on in the poem.