'To Autumn' is often interpreted as a peaceful evocation of the beauties of the English countryside, To me, it is more a subtle, troubled attempt by Keats to make some kind of sense out of dying young. It is hard to determine how much of this comes from a consciousness of his own impending death, and how much derives from more general thoughts about mortality. Nevertheless, it seems evident that the poem has a sense of conflict and ambiguity similar to the earlier, more obviously dramatic and questioning odes. The season of autumn is presented as a fertile and beautiful woman ('thy hair soft-lifted by the winnowing wind') but, as with other beautiful female presences in Keats's poems (La Belle Dame Sans Merci, the personified Grecian Urn, Lamia), the charm co-exists with a potential cruelty and indifference.
In his 1999 study of the effect on British literature of the diseases and climates of the colonies, Alan Bewell read "the landscape of 'To Autumn ' " as "a kind of biomedical allegory of the coming into being of English climatic space out of its dangerous geographical alternatives."  Britain's colonial reach over the previous century and a half had exposed the mother country to foreign diseases and awareness of the dangers of extreme tropical climates. Keats, with medical training,  having suffered chronic illness himself,  and influenced like his contemporaries by "colonial medical discourse",  was deeply aware of this threat.
She took me to her elfin grot,
And there she wept, and sigh'd fill sore,
And there I shut her wild wild eyes
With kisses four. And there she lulled me asleep,
And there I dream'd - Ah! woe betide!
The latest dream I ever dream'd
On the cold hill's side.
I saw pale kings and princes too,
Pale warriors, death-pale were they all;
They cried - "La Belle Dame sans Merci
Hath thee in thrall!"