To autumn

• "Maturing sun"

  .implies passing of time because the sun is getting older

  .shows the sun is setting on the harvest

  .also implies the sun setting in his life, because of his tuberculosis disease (TB)
• "Ripeness to the core"

  .implies an abundance of nature, nature had provided too much during the harvest

  .After fruit is ripe, it dies away, reminiscent of the passing of time which is uncontrollable

  .cycle will repeat, another harvest will be next year, the time will come around again
• "Drows'd with the fume of poppies"

  . Harvesting attacks the senses, smell, and sight, and touch

  .negative connotations

  .imagery of death when harvesting
• "Half reap'd furrow sound asleep"

  .implies that a field has been half harvested

  .tells us that even the farms are tired, all time and effort they have put into harvesting has exhausted them

  .the passing of time doesn't just have an impact on nature, but also people, they are powerless
• "Gathering swallows twitters in the skies"

  .migrating for the winter

  .represents keats transition to the end of life