This ode is almost like a pep talk delivered to autumn. The speaker knows that autumn often gets short shrift in the catalogue of seasons, so he reminds her (and, maybe, himself) of its many wonders: the bounty of the harvest, the dropping of seeds that will become next year's flowers, and the symphony of sights and sounds at sunset. Strangely, autumn herself seems blissfully unaware of any need to be praised or appreciated by anyone. She wanders through the scenery and examines her work without concern or urgency.
The poem's transition from mid-day to sunset parallels the transitions from summer to winter.
Despite the speaker's attentions, autumn neither wants nor needs his praise. Autumn's inaccessibility contributes to his awe.