In Of Mice and Men, what is the impact of Steinbeck's stylistic choices in its opening and ending?

Steinbeck was quite insightful in bringing out the idea of
George telling Lennie that if there was any trouble, he was to "go and hide in the brush."  This
was introduced in the opening, when things were tough, but not as complex.  It was also
introduced at a moment where hope was emerging to its zenith.  The dream of the farm had already
been introduced, and both Lennie and George had already been depicted to be different than others
of the time period in their sense of community and shared experience with one another.  In
bringing both back to the brush at the end, Steinbeck has been able to bring a sense of the
complete to the narrative:

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The most important symbol in the novel is the
bank of the Salinas River, where the novel begins and ends. In the story's opening, when George
and Lennie come to the riverbank, it serves as a symbol of retreat from the world to a natural
state of innocence. In this first scene, George tells Lennie that he should return to this
riverbank if there is trouble at the ranch where they plan to work. The riverbank is a "safe
place" for the two characters.

The fact that both the
opening and ending begins with a naturalist view of the small pond is meaningful.  At the start,
Lennie and George were concerned with drinking water and whether it was "clean."  Now, their
situations have grown in complexity and their problems are much more intense.  I think that
Steinbeck brings out this intricacy in Lennie, himself.  The vision of Aunt Clara and the rabbit
from his own mind help to enhance the fact that the world is having an adverse effect on Lennie. 
Additionally, Lennie's refrain of "going into a cave" is challenged by his visions, suggesting
that he would have never had the strength to leave George.  In the end, the narrative comes full
circle because of ending it where it starts.  There is almost a Classically tragic feel to it,
almost as if Steinbeck is giving his characters a sense of regal nobility that the real world
would never grant to them.  In this light, Steinbeck himself might be doing right what the world
had done intensely wrong.