Robert Frost's choice of language illustrates the concept/theme of a journey in his poem "The Road Not Taken." Word choice is a delicate art in poetry. Poets, and authors alike, pay close attention to how words sound when spoken aloud. They choose to use alliteration or assonance based upon how they wish a line of poetry to sound to the reader and listener.
The sound of words is also important when illustrating the importance of a concept or a theme. In regards to Frost's poem, his word choice illuminates the idea of the journey (in both direct and indirect ways).
For example, the following words illustrate Frost's direct nature regarding the journey: travel, passing, lead, took, and trodden.
As for Frost's indirect way of illustrating a journey, the following words/phrases illustrate this: wanted wear (illustrating something which wants to be traveled upon) and come back (illustrating a journey which has already taken place).