What is the contrast between art and life in "Ode on a Grecian Urn"?

Ah, one of my favorite controversial subjects to discuss about one of my very favorite poems EVER!

The contrast Keats creates between art and life in "Ode on a Grecian Urn" is precisely this:  that art is better than life (hence the title of the poem).  In fact, Keats proves this when he says, "Heard melodies are sweet, but those unheard / Are sweeter."  Why is art better than life?  Art, as in the form of the urn, can capture life at its best and keep it there.  Here is my favorite example:

Bold Lover, never, never canst thou kiss, / Though winning near the goal--yet, do not grieve; / She cannot faded, though thou has not thy bliss, / Forever wilt thou love, and she be fair!

Although ingeniously left unstated here, the contrast between art and life is quite vivid.  This lover can literally never kiss his love.  In life, they could kiss, yes, but that is not the real goal.  Keats even uses the word "winning" to prove that art is the true capturer of beauty here.  In life, this young lady's beauty would eventually fade and her lover's passion would fade as well.  Here I always imagine Keats exclaiming, "Not on this urn!"  This is literally the same point of so many poets:  that a love can remain eternal through poetry.  In Keats case here, through art.

Near the end of the poem, Keats even borders on jealousy of the urn, that will stand steadfast in beauty as the rest of the earth may waste away.  Keats even goes so far as to call it "Cold Pastoral!  When old age shall this generation waste, / Thou shalt remain."  Of course, the contrast between art an life is finalized in the final lines of the poem as well:

"Beauty is truth, truth beauty,"--that is all / Ye know on earth, and all ye need to know.

Truth, then (according to the highly debated last two lines of the poem), can precisely be found upon the urn (and not always necessarily in life).  Therefore art presents for us a utopia for the world to reside in its own way.