The Poetry of earth is never dead:
When all the birds are faint with the hot sun,
And hide in cooling trees, a vice will run
From hedge to hedge about the new-mown mead;
That is the Grasshopper's - he takes the lead
In summer luxury, - he has never done
With his delights; for when tired out with fun
He rests at ease beneath some pleasant weed.
The poetry of earth is ceasing never:
On a lone winter evening, when the frost
Has wrought a silence, from the stove there shrills
The Cricket's song, in warmth increasing ever,
And seems to one in drowsiness half lost,
The Grasshopper's among some grassy hills.
Keats, here, clues us in to the constant music of nature, which he calls "Poetry." The birds' song is poetry, though in the hot summer, when the birds "hide in cooling trees" we still have Poetry, we still have music. It becomes the domain of the grasshopper, who never ceases to delight in his own music.
"The poetry of earth is never dead" and "The poetry of earth is ceasing never" are the core image of this poem. In both day and night, summer and winter, the grasshopper and cricket provide us with poetry. The poem is filled with images of keen observation of sensation. Summer has "cooling trees" and the shade of some "pleasant weed." On a lone "winter evening" we have the Cricket's song, "in warmth increasing ever." Temperature, as well as mood, is expressed in both of these, and in both, we find comfort and pleasure. That comfort and pleasure is the poetry of nature represented by the songs of the grasshopper and cricket.