How does Steinbeck present the barn in Chapter 5 of Of Mice and Men, and why is it important to the novel?

Steinbeck's description of the barn in Chapter 5 is significant for several reasons.  First, Chapter 4 is also set in the barn, but it occurs at night in Crook's small room.  The author's description of the barn in Chapter 5 immediately follows the scene in which Curley's Wife threatens to accuse Crooks of attempted rape, and Crooks' decision to stay out of the farm dream plan. In Chapter 5, Steinbeck describes the light filtering through the barn's cracks. It is a sunny, restful day for most of the men.  Instead of hours in the field, most of them are playing horseshoes outside the barn in the bright sunlight.  In contrast, Lennie sits in the coolness of the barn, alone, with his newly killed puppy.  This different view of the barn in the chapter contributes to Steinbeck's overall light/darkness motif.

The quiet calm in the barn also contrasts well with the violent encounter between Lennie and Curley's Wife which occurs later in the chapter. After Lennie flees, and Candy and the others enter the barn to discover Curley's Wife's body lying in the hay, the barn begins to darken, and the Sunday laziness of the horses dissipates, foreshadowing the dark ending to come.