What are the main points of argument of "Keats Sylvan Historian: History Without Footnotes"?

Cleanth
Brook's essay "Keats's Sylvan Historian" is not merely a persuasive reading of Keats'
great poem "Ode on a Grecian Urn," but also a textbook example of the close-reading
strategy of New Criticism in action. Brooks revels in contradictions andin the poem, in contrast
to critics who insist on the poem's yielding up one straightforward meaning. Thus, problematic
aspects of the poem (such as the fourth stanza, in which the speaker imagines a town not
depicted on the urn, bereft of its residents who have travelled to perform a sacrificial rite)
defy "reduction to any formula."...