One of the main themes of Night is Eliezer's loss of religious faith. Throughout the book, Eliezer witnesses and experiences things that he cannot reconcile with the idea of a just and all-knowing God.
At the beginning of the narrative, Eliezer declares, "I believed profoundly." He is twelve years old and his life is centered around Judaism—studying the Talmud during the day, praying at the synagogue at night until he weeps with religious feeling. He wants to study the cabbala (Jewish mysticism), but his father says he's too young. Despite this, Eliezer finds a teacher in town, a poor man named Moché the Beadle, and the two of them pore over cabbalistic questions. Eliezer's faith in God is shared by many of his fellow Jews in the town of Sighet. On the trains to the concentration camps, people discuss the banishment from their homes as trial sent from God to be endured—a test of faith.
But Eliezer's belief in God begins to falter at the concentration camps of Birkenau-Aushwitz. Here the furnaces are busy night and day burning people. Here he watches German soldiers throw truckloads of babies and small children into the flames. The longer he stays in the concentration camps, the more he sees and experiences cruelty and suffering. People treat others worse than they would livestock. He can no longer believe that a God who would permit such nightmare places to exist could be just. The fact that many Jews do continue to pray, to recite the Talmud, and to look for comfort in their faith while in the concentration camp amazes and confounds Eliezer. That people would still pray to a God who allows their families to be gassed and incinerated suggests to Eliezer that people are stronger and more forgiving than the God they pray to. Later, as more people die, and others around him lose hope, starve, and succumb, Eliezer ceases to believe that God could exist at all. He is not alone in his disillusionment. Akiba Drumer (whose faith helps Eliezer endure for a while) as well as a rabbi whom Eliezer talks to, also eventually come to believe that God's existence is impossible in a world that contains such a large-scale, willful horror as the Holocaust. The final nail in the coffin, for Eliezer's faith, comes at Buna, where the prisoners are gathered to watch the hanging of a young boy. A man in the crowd asks, "Where is God now?" Eliezer's internal response is that God is that boy on the gallows. The boy dies slowly as the prisoners are forced to watch.