How we cite our quotes: (line)
Quote #1
Of beechen green, and shadows numberless,
Singest of summer in full-throated ease. (lines 9-10)
The nightingale is in its prime, and the natural things around it are in the peak of their goodness. Keats's poetry often focuses on the transience of the seasons, and especially his odes, like "To Autumn" and "Ode on a Grecian Urn," which describe fall and springtime, respectively. This ode captures the glory of summer.
Quote #2
Where beauty cannot keep her lustrous eyes,
Or new Love pine at them beyond to-morrow. (lines 29-30)
Out with the old, in with the new. For the speaker, this adage captures all that's wrong with the world. People never have time to savor the good things. Beauty and love always seem immortal, but after "to-morrow," they might be gone forever. The poem seeks an escape from time.
Quote #3
But, in embalmèd darkness, guess each sweet
Wherewith the seasonable month endows (lines 43-44)
The nightingale's world is dark, but it still captures the peak of summertime. Summer is "seasonable" because all the plants and flowers (those "sweets" he refers to) are out in full force. But this world is not transient; it is "embalmed" with the scents, like a tomb. Death – now there's one way to escape time.