Jimmy and Bob act as foils for each other in this story, meaning that their juxtaposition in the story reveals important qualities of each of their characters. In particular, readers are meant to notice how moral and reliable Jimmy is, especially when compared to Bob, an untrustworthy criminal willing to harm others for self-gain. Bob himself seems to be aware of these key differences between him and his childhood friend, as he explains in the following passage:
“Did pretty well out West, didn’t you?” asked the policeman.
“You bet! I hope Jimmy has done half as well. He was a good kind of plodder, though, good fellow as he was. A man gets in a groove in New York. It takes the West to put a razor-edge on him.”
Here Bob describes Jimmy as a “plodder,” or someone who works slowly and methodically, while implicitly describing himself as someone with “a razor-edge.” This does seem to be the case, given the fact that Jimmy still lives in his old neighborhood and is a meticulous police officer, while Bob moved west and got embroiled in criminal activity.
In making these men so different from each other (and in having Jimmy betray Bob by having him arrested at the end of the story), O. Henry communicates that time and geographic distance can further the emotional distance between people as they both change, and can thereby alter their relationship and their loyalty to each other.