There are several ways in which the figurative language Frost employs to help illuminate the meaning. In order for this to be established, I would point to the meaning of the poem in terms of choice and freedom being the crux of what it means to be human. Finding specific lines and references to this would be good as the poem is filled with them. In discovering these lines and references, examine how Frost is discussing the theme of freedom of choice. For example, the figurative language used to describe the paths themselves. Finding the specific word choice, specifically in the second stanza, helps reveal why the speaker made the choice he did. The images employed help the reader to understand why the speaker made the choice he did, central to the meaning and purpose of the poem.
The Road Not Taken by Robert Frost is one of the most comprehensive instances of a poem written in purely figurative language. Language of poetry is always figurative or metaphorical in terms of the symbolic import of its images. But Frost's poem is all the more figurative simply because it operates entirely on a universal and strictly non-particular level of the generic. There is no spatio-temporal reference, no periodization, not a single proper name in the poem. The realistic metonymic style is given up for a completely metaphoric or figurative style. This poem can only work at the level of the figurative/ the allegorical.
Some specific instances are
1. Yellow wood--the colour may signify nostalgia, pain or even old age as in retrospect. It is also a figure for human experience in all its cognitive import.
2. undergrowth-- a very complex abstract figuration of a space that we tend to create for ourselves to peep into life. These are intended to be viewpoints that are extricated from the mainstream of life and thus give us the critical distance from which we can read life and its trajectory.
3. The idea of the wear and tear on the road is a figure for the rough and tough up-n-down ride of human life
4. The last line and the idiomatic expression that has made all the difference is used in such an open and ambivalent manner that it becomes a perfect example of exclusively figurative language.