Many questions regarding poetry are subjective. What this means is that the question's answer is based upon a reader's interpretation of what something means. This question is no different. The answer rests on what how a person interprets Frost's poetry, how they interpret his use of themes, and what one understands the quote to mean.
Therefore, the answer the this question relies wholly upon how one interprets the quote.
Poetry is meant to be examined. Poetry is meant to evoke feeling. Poetry is meant to become lost in; in regards to text and thought. Therefore, to do this, one must stand on top of the poem. To gain complete understanding, one needs to step back and look at the impact the poem has as a whole on the reader.
What one could interpret the function of the poet in regards to "one step backward taken" as being representative of looking at the whole picture of what is being described, pondered upon, and reflected.