On Ode on a Grecian Urn, John Keats, explores the relationship between ideal beauty and the real changeable reality of the everyday humans life.
In this poem, the author gazes at the picture of an ancient greek urn, which in Greece were used to hold the ashes of the dead. He used to believe that greek art in general was idealistic and virtuous and this was the poem's basic theme.
The thought he exposes in the first stanza is the supremacy of ideal art over Nature, because of its unchanging expression of perfect.