Critics through the ages have been troubled by these last two lines of this wonderful Ode, as they seem on the surface at least to have very little to do with the rest of the poem and the depiction on the scenes of this Grecian urn that Keats so powerfully visualises for the reader. However, it is clear through this statement that Keats is actually making quite a philosophical comment about truth and beauty. One way in which this statement can be interpreted is to consider that the scenes on the urn are true and beautiful because they are frozen in history and therefore separate from the messy reality of day to day living. Note how the final two lines are mentioned in a context that draws the reader's attention to the eternal nature of art contrasted with the ephemeral nature of human experience:
When old age shall this generation waste,
Thou shalt remain, in midst of other woe
Than ours, a friend to man, to whom thou say'st,
"Beauty is truth, truth beauty"---that is all
Ye know on earth, and all ye need to know.
The Grecian urn becomes a powerful symbol of permanence when compared with the mortal lives of humans, and Keats therefore uses this urn as a symbol of beauty because it is self-contained and frozen in time. By contrast, the lives and experiences of humans are never self-contained and constantly lack answers. The poem therefore points towards a divide between art and experience, and suggests that such truth and beauty can never be fully captured in real life. Humans are left to appreciate such flawless truth and beauty in the form of art alone.
In the concluding part of Ode To Grecian Urn , the urn unlocks to an artist the mystery of art .What the Urn means to say is that , art evokes imagination , and imagination leads one to the realm of beauty ,and when one grasps the beauty , then he realizes the truth .Beauty and truth are inseparable .Imagination sets a link between them .But , without art , imagination would not find any passage of its reflection .