What is the main idea of The Devil's Arithmetic by Jane Yolen?

The main idea of this book is to reveal (and remember) the horrors of the Holocaust from a young adult point of view.  The main character, Hannah, is annoyed greatly by her Jewish faith as she travels to her grandparents’ house to eat the Seder meal.  During the meal, Hannah is transported back in time to 1942.  She finds herself part of a Jewish family and is suddenly called “Chaya.”  While entering the synagogue for a wedding, Hannah/Chaya and all of the other Jewish people are herded onto trucks and sent to a concentration camp.  This is where the horrors begin.  Women and children are sent to the gas chambers.  Others starve to death.  Still others are worked to death.  The story of Chaya is a tale of great bravery.  Chaya sacrifices herself for her friend Rivka when Chaya enters the gas chamber in Rivka's place, telling her to both “run” and “remember.”  This book is Chaya’s story.  As a result, the victims of the Holocaust are remembered in a very moving way.