What is the evolution of thought in ode to a nightingale?

"Ode to a Nightingale" by John Keats explores the themes of mortality, nature, and the tension between ideal beauty and harsh reality. The poem traces the speaker's journey from enchantment with the nightingale's song to a realization of the fleeting nature of human existence and a longing for escapism from the pains of earthly life. Ultimately, the poem concludes with a bittersweet acceptance of the transience of beauty and the inevitability of death.