The poem reflects the poet's belief that the beauty of nature never ends--in the summer, that beauty is heard in the grasshoppers call; in the winter the beauty of nature is shown by the shrill of the cricket.
Viewed metaphorically, Keats is suggesting that although we easily recognize the beauty of life in youth, there is also plenty of beauty in old age.
Viewed metaphorically, Keats is suggesting that although we easily recognize the beauty of life in youth, there is also plenty of beauty in old age.