What is the summary and main theme of "Birches" by Robert Frost?

Like much of Frost’s poetry, “Birches” takes a look at the interaction between nature and man. In this case, we have a grown man, the narrator, telling the reader that he recalls what it was like to swing on birch trees when he was young. As an adult, he knows that birch trees are bowed because of the ice that bent their trunks in the winter, but he prefers to think that, like he did as a youngster,

some boy’s been swinging them.

The memory of birch swinging is a release from the cares and trials of adult life, a sort of freedom that takes him back in time. Notice that when Frost describes the problems associated with adult life, he continues to use natural imagery:

It's when I'm weary of considerations,

And life is too much like a pathless wood

Where your face burns and tickles with the cobwebs

Broken across it, and one eye is weeping

From a twig's having lashed across it open.

Thus, as we grow, play and adventure is replaced with pain, danger, and weariness.

Frost concludes with something of an understatement in the poem’s final line:

One could do worse than be a swinger of birches.

This emphasizes Frost’s point that interacting with nature in a playful way is actually more rewarding than the responsibilities that accompany adult life.

In good writing there are usually numerous possible themes. It depends on how the reader perceives the work. In “Birches” we might say that the theme is something like “the memory of the joy of youth is a relief from the cares of adult life.” Or, if one preferred to work the idea of nature into a theme, we might say, “The interaction of man and nature imbues our lives with more meaning that the expectations of society.”