The poet and biographer Andrew Motion suggests that this Ode makes a 'calculated inquiry into the function of art—and of its relation to life'. In the ekphrastic tradition, the poem celebrates the beauty of an ancient Greek artifact; except that there does not seem to have been an actual original. Keats appears to have absorbed and amalgamated several different original objects, and created an imaginary urn to use in his poetry—another paradox to add to the many incorporated within the Ode.
One such paradox is the attempt to deal with a plastic, visual object in the verbal terms of poetry. Whereas the urn is an object in space, the poetry which interprets it must be read in a sequence through time, and is thus connected to time in just the way the urn is not. The urn represents frozen moments; the Ode gives them context.
Within the verses are a series of opposites. The urn portrays frozen images of dynamic life—'mad pursuit', 'maidens loth', 'wild ecstasy', the Bold Lover close to a kiss, the heifer being led to the sacrifice. The verses point up the contrast between these immortal, permanent images and the changeability of human life by presenting the contrast forcibly: the 'happy, happy love' depicted on the urn is 'For ever warm', but human passion, reality
"leaves a heart high-sorrowful and cloy'd
A burning forehead, and a parching tongue."
The tension inherent in this contrast is vital to the poem: in the object of art, knowledge of human sorrow is held at bay. The depictions are caught at the moment of perfect balance, not quite achieving the bliss that cannot but be transient and lead to pain. Yet for the poet, and his readers, human suffering, and the passage of time, are familiar experiences and essential to existence.
Keats is thoroughly aware of the joy and pain, the happiness and sorrow, of human life, and that these things are inextricably joined together. Yet the urn he depicts shows scenes and people who are essentially untouched by suffering, and will forever remain so. The urn is poised in time, and also timeless.
The urn exists (or, is represented as existing), and thus must in some sense be 'in time'. It is addressed as 'still unravish'd bride of quietness'; that 'still' represents both time and (lack of) motion. The urn is unmoving, obviously, but there is also a subtle implication of 'as yet' and also of 'even after so long', which seems to place the urn in almost the same state of expectation that applies to the figures upon it. Then again, the urn is divorced from time—its original era is long past, its creators are dead. Though the urn itself has not deteriorated, and may thus be viewed as immortal, it is also a reminder of death, and indeed such words as quietness, silence, and slow time, can be very much associated with death. It the urn in fact a funeral urn, even though Keats does not say so? The fourth stanza is explicitly associated with death: there is to be a sacrifice. From there on, the poet expands his imagination beyond what is depicted, and supposes a deserted settlement, left empty by this procession which will never return—again a reminder that the urn is from a long-past era, and that the civilisation and the people who created it are dead.
The poet then projects the urn forward in time: its silent enigma will still exist when his own generation is gone, and its message will still be there for future men to ponder.
The chiasmus 'Beauty is truth, truth beauty' seems to be the message from the urn itself. However, as J Stillinger says, "as to critical interpretation of who says what to whom, no single explanation can satisfy the demands of text, grammar, consistency and common sense." I think this may be the point. Susan Wolfson describes Keats as writing the 'poetics of co-operation'. He does not 'pre-resolve' his issues, but invites the reader to find his way to an understanding of them. Perhaps 'negative capability' is necessary for the reader as well as for the poet. So do the last two lines mean that there is no need to speculate, as the poet has been doing, on the feelings and situations of the figures on the urn—that their beauty is sufficient in itself, and can be understood simply as beautiful? Do the lines reflect on the cold self-sufficiency of this object? Is it that the urn's limitations are being pointed out—that the only lesson it can teach is that of timeless beauty, and that therefore it can offer no greater message? Andrew Motion points out that these lines are "evidently not all that mankind knows on earth, or needs to know, and neither do they adequately encapsulate Keats's artistic ambitions". It is not necessary for the reader to 'know' what the poet 'meant', it is more important to rediscover possibilities when re-reading the poem.
In any case, although the final two lines are particularly intriguing it is more to the point to see the poem as a coherent whole, which reminds us that life is simultaneously like and unlike art, dramatising a response to an artistic work, and 'teas[ing] us out of thought' and into our own individual response.