To bend with apples the moss'd cottage-trees, And fill all fruit with ripeness to the core; (lines 5-6)
The transformation into ripeness proceeds slowly, as the branches bend more and more under the weight of the growing apples. The speaker imagines this process as the outcome of secretive plans between autumn and the sun.
Who hath not seen thee oft amid thy store? (lines 12)
The second stanza moves subtly from ripeness to the harvest process. While the first stanza was centered on fruit and nuts, which are more like luxuries, the second stanza focuses on grains, the most essential food staple.
And sometimes like a gleaner thou dost keep Steady thy laden head across a brook; (lines 19-20)
The poem moves through the different events of the season without the reader hardly noticing. At the end of the stanza on harvesting, Keats compares autumn to a gleaner who picks the last bits of grain left on the field.