One can read a poem from multiple or differing perspectives and come up with different themes for different people or circumstances. But if we look at Frost's poem "The Road Not Taken " from the position that humans are defined by the choices they face and ultimately make, then...
One can read a poem from multiple or differing perspectives and come up with different themes for different people or circumstances. But if we look at Frost's poem "The Road Not Taken" from the position that humans are defined by the choices they face and ultimately make, then the speaker of the poem can represent all of us as we face any number of choices in life.
More specifically, though, it seems that not many people actually have to face these two ambiguous choices, because he claims that both paths are still "grassy and wanted wear," which means that not many have traveled either path, but he is considering them both. One might infer that the speaker is a pioneer of sorts, which means that others may ask his advice on these paths in the future if he takes one of them. For example, he says, "I shall be telling this with a sigh / Somewhere ages and ages hence."
Then, if people will be asking him about it later, this means that it is a pretty significant choice that he will be remembered for and therefore "defined" by it.
As a result of future generations being affected by this choice, whether that be mankind or only the speaker's posterity, it matters to him that he considers both options as best as he can based on the limited information that he has in front of him. For instance, he shows that he considers both paths intently by saying, "Yet knowing how way leads on to way, / I doubted if I should ever come back." This shows that the speaker is mature enough to recognize that coming back to this point in life again will never happen and, because of the way life branches out before us every day, this choice of which path to take now becomes more important than just a stanza before.
This is the best we all can do when faced with choices that we aren't sure about and don't know where they will take us in life. All we can do is make the best choice we can with the information that we have right in front of us. This is a very relatable example of the human condition!
And just to drive home the fact that choices we are faced with and make are important, he doesn't tell us which path he took, or how it "made all the difference," because that is for each of us to find out for ourselves as we journey through life on our own.