The first line of the poem "Seasons of mist and mellow fruitfulness" suggests that autumn is a season of change but despite this, it is a calm season
By personifying autumn in 'Thee sitting careless on a granary floor,' it suggests that autumn can be quite thoughtless in the changes it brings
Keats continues to personify autumn and addresses it directly in 'thou watchest oozings,' implying that autumn 'behaves' as if it has all the time in the world even though time is passing by
The last line 'And gathering swallows twitter in the sky' shows that winter is drawing in and time is coming to an end – it could represent the circle of life