He says in the poem, “ripened to the fall,” implying two separate meanings: 1) he notes that the leaves are changing color because of the autumn season, 2) the leaves have a purpose of growing and that is in order to fall off and die.
He uses the words, “To-morrow they may form and go” to explain that nothing in nature or in the world will stay forever.
He speaks about the transient nature of life and the ever-changing sphere of nature.
No matter what he is describing, he conveys a special feeling of some intensity.
He has a special gift of making what is personal to him personal to others.