I'll admit, I haven't been looking forward to this Song -- Song 6. It's dense with allusions. This is one I'm struggling to comprehend fully. Find it at the following link:
This Song is only one sentence. Although I am a fan of long sentences, whenever a poem employs one, the reader better be prepared for a mind-bender.
The title alludes to Wells Cathedral in England. The "capitals" addressed being those points that stick out at the top of the towers, crafted in what is known as "stiff leaf" style. An aside: this is the church in Hot Fuzz.
I want to say this poem stands, like the great cathedral, between Henry and himself, or somewhere in the periphery. There is Henry's lust, and now we see the face of God on earth.
The first stanza I relate to Berryman's father. However, I see the pun between Berryman's father and the Catholic "father." Berryman identifies with his father's breaks and ill-luck, comparing himself and his father to Ethan Allen, one of the founders of Vermont, also a prominent businessman.
Berryman, with the lines "Keats sweat' / for hopeless inextricable lust, Henry's fate," shows us that Henry will struggle with his lust until his death (and after it).
I'll do my best to give you the keys to the poem, so you can continue to think about it, since I don't have it all figured out. Aeneas is a figure in Roman mythology, who was a founder of ancient Rome. Why the cardinals wanted to keep him out, or why "Chinese doubt / inscrutably was growing," I can't discern.
Peter Abelard, mentioned in the second to last stanza, was a brilliant philosopher during the Middle Ages, who castrated himself because of his failed love affair with a woman named Heloise. Henry himself is similarly mutilated in a Song to come, at least figuratively, if not literally.
The grapes proffered in the final line are those spheres on the very top of each capital.