The central moral theme of the story involves the distinction between murder and hunting. Rainsford sees a clear difference between the two, hence his disgust at Zaroff's hunting of men. Zaroff, on the other hand, sees his pastime as similar to a war.
This particular theme remains a source of tension throughout the story. As Rainsford is hunted, he does his best to try to destroy Zaroff through a series of traps. In the end, it is implied that Rainsford has proven to be the greater hunter. Rainsford's last line of the story indicates that he slept in Zaroff's bed. Such an action can be read as a metaphor for his unwilling conversion into a hunter of men.