A writer's purpose can usually be found in the themes that he develops in his work. In Elie Wiesel's Night, there are several themes that run throughout the work.
When Wiesel writes about the cruelty of the Nazi soldiers in the concentration camps, he is developing the theme of man's inhumanity to man. This becomes poignantly evident when we see changes in Elie himself. At one point he tells the reader that because of his hunger and deprivation, he had become nothing more than "a stomach."
However, Wiesel also develops a counter-theme of kindness under severe conditions. Despite the suffering and ever-present threat of death, there are still moments when people are kind and giving. At one point, a young violinist named Juliek, who somehow managed to hang on to his violin in the midst of forced marches, plays beautifully for the exhausted and dying prisoners, only to die himself soon after. Elie's father continues to give Elie his own rations as he faces starvation himself. Sometimes prisoners risk their own safety to give comfort to those who are suffering.
Wiesel's main purpose is no doubt to ensure that the world knows what happened in the camps. His own characters persistently denied their fate early in the book, refusing to believe the things they had heard about the Nazis' plans for them, refusing to believe that such terrible things could happen to them in the twentieth century. Wiesel wants to make sure that the rest of the world doesn't make that mistake.