Critical commentary on Sir John Betjeman's 'In Westminster Abbey' - composition of essay

The poem can be found here:

http://www.research.att.com/~jrex/faves/poems/abbey.html

I have to write a critical commentary on "In Westminster Abbey" by Sir John Betjeman. I'm having a problem with the composition of the essay - i'm not sure what rough line of argument i should take.

Thanks for any help.