The most important events in The Devil’s Arithmetic are Hannah’s transportation to the past, and her experiences in the Holocaust.
Hannah is just an ordinary American teenager who happens to be Jewish. She does not see her religion as an important part of her heritage, and instead she just finds most of the observances a bore. When she is transported back to the Holocaust in the form of Chaya, her Hebrew name, she is forced to come to terms with her identity and who she really is.
"She was not Hannah Stern of New Rochelle, at least not anymore, though she still had Hannah's memories" (ch 8, p. 63.)
As she experiences the horrors of the concentration camp, Hannah finds an inner-strength she did not know she had. She begins to stand up for others, and think of other people before herself. She also realizes that she might die, because she alone knows what is going to happen. This experiences helps Hannah grow, and soon she sacrifices herself to save her friend Rivka. She now fully understands her family history, her name, and her heritage.