One of Keats' themes is the contrast between people and situations frozen in perfect representations and living people and evolving situations that are imperfect. On the urn, the bride and groom are represented as forever lovely and forever in love in stanza 2: "For ever wilt thou love, and she be fair!" In stanza 3, the trees of the woods and the musicians have "[m]ore happy love" because they will never "bid Spring" farewell nor ever grow weary of piping their song: "melodist, unwearied, / For ever piping songs for ever new." The procession, most likely the wedding procession leading both guests from the town and the young female cow to be sacrificed to the Hymen, is captured forever marching the garland draped cow to a "green alter."
The contrasts in stanza 2 to real living people and evolving situations is that in real life, pipers will write new songs, grooms will kiss their brides, brides will be "ravish'd" on the hoped for wedding night even though both will grow old and love may fade. In stanza 3, "Spring" will turn to fall while human passions are enjoyed even though they yield "A burning forehead, and a parching tongue." The town, the "the peaceful citadel," from which the procession departs will not know the return of its inhabitants and be forever "desolate." It is these contrasts that lead Keats to accuse the urn of "[teasing] us out of thought / As doth eternity."