context: keats was a romantic poet and wrote a lot about the natural world, died at 25 worried he'd leave no impression of the world so this poem could be an attempt to leave his mark and be remembered
structure: first stanza is a celebration to suggest autumns begins in a rich and calm way. final stanza shows change, as it goes from autumn to winter. Keats accepts this fact he cannot control this
"mellow fruitfulness!" - 'mellow' suggests that autumn is calm ad the changes aren't disruptive
"and gathering swallows twitter in the skies" - could suggest Keats is ready for death and to 'move on' just as the 'swallows' are 'gathering' to warmer climates