Both men are steadfast friends, but Bob is a criminal and Jimmy is a cop.
Both Bob and Jimmy are described physically. First, Jimmy is described.
[The] officer, with his stalwart form and slight swagger, made a fine picture of a guardian of the peace
The Bob is described.
The light showed a pale, square-jawed face with keen eyes, and a little white scar near his right eyebrow
There is a stark contrast between Bob and Jimmy, yet they both came from the same place. In a way, the story is about different paths we all have. Jimmy chooses to stay behind and follow the straight and narrow, while Bob is ambitious and hopes to make his fortune. Bob actually falls into the American metaphor of going west and becoming rich. Sometimes that involved less than virtuous activities. Jimmy becomes the law, and Bob becomes the law-breaker.
Bob arrives first. Jimmy makes his way in a leisurely way. Is this because he suspects that Bob might have become less than savory over the years?
Bob seems nice enough.
"It's all right, officer," he said, reassuringly. "I'm just waiting for a friend. It's an appointment made twenty years ago. Sounds a little funny to you, doesn't it?
He kept the appointment. So did Jimmy, but Jimmy still lived nearby. It was more a stretch for Bob. Why did Bob return? It shows that he was willing to risk going back where he may be recognized, because he wanted to be faithful to his friend.
Bob describes Jimmy as a "plodder" and says he never would have left New York. Being a cop is very important to Jimmy. His “impressiveness was habitual and not for show” and he walks down the street checking doors to make sure they’re locked. He cares about his neighborhood and his role. Yet he also cares about his friend. He cannot arrest him himself, so he gets another cop to do it. He is not willing to break the law and let his friend go, but he has not the heart to arrest him himself.