How is the beauty of nature blended with wisdom of a matured person in the poem "Birches"?

In line 41, the speaker recalls that "I [was] once myself a swinger of birches." He reflects upon an earlier time in life when boyhood joy, a sense of carefree exploration, was wrapped up in the nature around him.
Once upon a time, he was free to exist in a world where a successful climb to the top of a tree was the goal of the day. And now, he "dream[s] of going back to be" in this state of a carefree existence in nature. He notes that he has these reflections "when [he is] weary of considerations, / And life is too much like a pathless wood." In adulthood, he finds that he is consumed with responsibilities and obligations.
Sometimes in life, there is no clear path to take, and adults have to find their own way through often-confusing life choices. This stands in sharp contrast to the path directly up the tree of childhood, when obligations are few and choices seem pretty easy.
Frost uses the metaphor of a twig that has lashed his eye to symbolize the painful experiences that life can bring as adults try to find their way in these "pathless wood[s]." The speaker uses images of nature primarily as a link to the beautiful magic of childhood years, and, looking back, he longs to "climb black branches up a snow-white trunk / Toward heaven" once more.