An ode is a poem dedicated to something or someone and is generally very exalted and lofty. Keats is a poet whose odes have gained a lot of fame. A specialty of his odes is that most of them talk about achieving the 'ideal'. This ideal, according to Keats, is perfection in beauty. Keats used characteristically Romantic themes in his odes; nature, the imaginary world, and the transient nature of human life, versus the immortality of the 'ideal'. Keats uses many such paradoxes in his odes.
In Keats's odes, the narrator is continuously pursuing perfection. Keats believed that this perfection did not exist in the human world, and could be found only through one's imagination. A common theme in his odes is of a perfect object transporting the narrator or protagonist into the imaginary world. In the Ode to a Grecian Urn, Keats has portrayed the urn as a perfect object. He has implies that perfection and beauty can only be found in nature, and in art. The urn is therefore a symbol of the perfection Keats sought to achieve. Throughout this poem, the urn is apostrophized, as seen when the narrator addresses the urn directly, 'thou foster child' and 'thy song'.
Keats also compares the urn to various things. In the very first line, he calls the urn an 'unravish'd bride'. At a literal level, this means the urn is in pristine condition; undamaged and whole. But it also links to an almost virginal purity of the urn. It is untouched by others. This can be connected to an image on the urn, of the two lovers. They are separated from each other, implying unrequited love. The lovers can never touch, as they are frozen images on the urn. Thus the woman is untouched and pure, just like the urn. The idea unconsummated love is further strengthened by calling the urn a 'foster-child'. It states that it is not born through a physical union of 'silence and slow time' and is thus 'unravish'd'.
Another theme present throughout this poem, and other odes in the Romantic period, is nature. Nature is always present in Romantic literature, as a theme, setting or in the form of symbols. In Keats' odes, the ideal is often something in nature; such as a nightingale or autumn. In Ode to a Grecian Urn, however, the subject of the poem itself is not a thing in nature. It is a piece of art, but the depictions on the urn are based on nature. It is called a 'Sylvan historian', thereby linking it to forests, and nature. The urn has a 'leaf-fring'd legend' and trees and other natural elements depicted on its surface. Thus Keats uses nature imagery in his poem. Also, the mention of 'Arcady' signifies rural simplicity and natural surroundings. The most important reference to nature, however, is the 'pastoral'. A pastoral refers to a quiet, village lifestyle with nature at its heart. It provides an escape from the hectic city life to a peaceful, natural setting. Though seemingly a positive word, Keats has termed it as 'Cold pastoral!' This oxymoronic statement has multiple interpretations. First, at a literal level, the depiction of the pastoral is 'cold' as it is frozen on marble and therefore unchanging. But 'cold' could also show Keats' frustration at the immortality of the urn. Human life is transient, and gets over soon, but the urn lives on for many generations. When Keats' wrote the poem, he was diagnosed with tuberculosis. Hence the use of 'cold' could show his dissatisfaction with a mortal human life; and jealousy of a perfect or ideal life of art.
Keats often explores the immortality of beauty and perfection versus the temporary, mortal nature of human life. In Ode to a Grecian Urn, this theme is altered slightly. This is done by inscribing mortal humans on something that lasts forever; the urn. Human life is given permanence by showing it on the urn. Thus the urn bridges the gap between mortality and immortality; it forms a connection between the two.
The narrator in the poem is human, and hence must eventually succumb to death. But the urn will live on.