Here, on the Poetry Foundation website, is an excellent interpretation of The Road Not Taken, one of the most misunderstood of poems. An excerpt:
Through its progression, the poem suggests that our power to shape events comes not from choices made in the material world—in an autumn stand of birches—but from the mind’s ability to mold the past into a particular story. The roads were about the same, and the speaker’s decision was based on a vague impulse. The act of assigning meanings—more than the inherent significance of events themselves—defines our experience of the past.
In a letter, Frost claimed, “My poems … are all set to trip the reader head foremost into the boundless.” The meaning of this poem has certainly tripped up many readers—from Edward Thomas to the iconic English teacher in Dead Poets Society. But the poem does not trip readers simply to tease them—instead it aims to launch them into the boundless, to launch them past spurious distinctions and into a vision of unbounded simultaneity.
There is a level of Sartrean existentialism to the poem. Of course written decades before Sartre's work.