What is the importance of the stone and the bell in Act2 Scene3

He talks as if talking to the class, saying his lessons were meant to help them in life, and will be useless if they are dead. Someone throws a stone and it breaks the window. Mr. M starts to ring the school bell loudly again. Thami appears and tells Mr. M to stop ringing the bell, saying he is "provoking the Comrades" (p.68) by openly defying the boycott. Mr. M says he is ringing the bell because he rings it at the end of every lesson, and he asks if Thami has come back only to tell him to stop ringing the bell or if he has come for a lesson. When Thami says that he didn't come for a lesson, Mr. M agrees that you don't need to know grammar to write slogans or throw rocks. He picks up his dictionary in one hand and the stone that came throw the window in the other; he ruminates on how the stone is only one word while the dictionary holds the whole English language. Suddenly, he offers the book to Thami; Thami ignores this gesture.