Wiesel is primarily trying to show how man can mistreat and dehumanize other men by their actions. In his case, he is deprived of his home, family, and dreams by Nazi Germany in World War II.
At the beginning of the book, Wiesel strongly emphasizes how important Wiesel’s religion (Judaism) is to him. He wants nothing more than to learn as much as he can about it. However, as the story progresses, and Elie begins to suffer, we see him begin to revolt against God. At one point he even questions why he should pray to a God that allows such suffering. He often refuses to pray at all, emphasizing the fact that, after being in a concentration camp for awhile, all he cared about was his stomach.
The deterioration of Wiesel’s religious faith is just one of the themes in the book, but it serves to show how mankind can strip others of the things that define their humanity.
It is important to understand that Night is the first book in a trilogy comprising Night, Dawn and Day. Together, these narratives reflect Elie Wiesel's state of mind during and after the Holocaust. The titles mark the author's transition from darkness to light, according to the Jewish tradition of beginning a new day at nightfall.
In this context, Night represents the nadir, or point of deepest despair, of Wiesel's journey into darkness. "In Night," Wiesel explains, "I wanted to show the end, the finality of the event. Everything came to an end—man, history, literature, religion, God. There was nothing left." (Reichek, Morton A. "Elie Wiesel: Out of the Night," Present Tense. Spring 1976, 46).