Death
Autumn, in spite of the season's festive colors and beauty, ultimately signals a process of death and decay. Even as the figures and images identified by the speaker signify the season's languor and livelihood, they also represent the peak of life—a point that signals imminent decline. The tree branches may be filled with ripe fruit, but soon this fruit must be picked, then the leaves will change color and fall to the ground. Likewise, the youth who naps on a hay bale must eventually wake up.
Transitions
"To Autumn" is also about change, or the process by which one state of being enters or becomes another. As the speaker observes the season's culmination of life, he also recognizes the first subtle traces of change in the natural world as it prepares for winter. The speaker, by contemplating the world around him, comes to accept the inevitably of time's passing, and realizes that he should savor the beauty the season can offer, instead of wishing for, or looking back to, warmer days.
Beauty
By the end of the poem, the speaker recognizes autumn's particular beauty. Why mourn the lush landscapes of spring and summer when autumn, as he says, has its own music?
Nature
Keats creates a parallel between the cycles of decay in the natural world with the inevitability of death in mankind. Nature functions as a backdrop for the poet's ruminations on time, death, and happiness. Just as life reaches its sweetest point, it begins its downhill spiral. But nature, like man, is infinitely renewed: seasons pass and return, just as death is balanced by new life.
Innocence and Experience
Throughout the poem, the tension between innocence—the superficial joys one experiences through autumn's bounty and beauty—and experience—the knowledge that all of its fruits will soon be picked, that all of the colorful leaves will fall to the ground and decay—expresses both the speaker's skepticism towards the leisure and pleasure he witnesses around him, and his acceptance that these feelings of happiness and melancholy can coexist. By the end, the speaker's realization that he can see the beauty for what is, regardless of its transience, demonstrates wisdom, not ignorance.
