Robert Frost's "Birches" is a rather nostalgic and rueful conversation between the speaker and the reader, whom he addresses as "you." With the metaphor of swinging, the speaker takes the reader through a series of "swings" from the imagination to reality. He begins with a flight of fancy:
When I see birches bend to left and right
Across the lines of straighter darker trees,
I like to think some boy's been swinging them.
But, realistically, the speaker knows it is ice storms which have crippled these limbs although his imagination wishes to reject the reality and return to his youthful innocence:
But I was going to say when Truth broke in--...
I should prefer to have some boy bend them...
Whose only play was what he found himself,
Summer or winter, and could play alone.
To swing freely as he has done in his youth would release from the speaker some of his earthly burdens as he would transcend the mundane--"when I'm weary of considerations"--and imaginatively return to his boyhood innocence. Lines 41-42 express this loss of innocence:
So was I once myself a swinger of birches,
And so I dream of going back to be.
In reality, though, the speaker knows that "Earth's the right place for love" and he must accept his current station in life as a man despite his yearning "to go by climbing a birch tree." After all, "One could do worse than be a swinger of birches"; one needs that innocence of youth.