That author believes that the situation is without hope, so he was no reason to continue one.
Rainsford's actions are justified because he will never truly be free until Zaroff is dead. A "beast at bay" refers to someone who is still being hunted. Rainsford will always feel hunted as long as Zaroff is alive, because he knows the 'hunt' will always go on in Zaroff's mind. He has to kill Zaroff so he doesn't have to live in fear.
Emphasis means “special importance, value, or prominence given to something.” or stress laid on a word or words to indicate special meaning or particular importance. An example is a baby learning how to talk in a month and have a lot of emphasis on her. Emphasis can also mean to focus or like bring attention also surprise.
