What does night symbolize, as a theme and idea, in Elie Wiesel's novel Night?

The title of Elie Wiesel's book Night is no accident, as night is used symbolically throughout the story. Night, of course, is dark, and its use in this story is no accident' it represents the loss of innocence, the loss of life, and the loss of faith.

The most recognizable passage in this story occurs the night Elie arrives at the concentration camp.

Never shall I forget that night, the first night in camp, which has turned my life into one long night, seven times cursed and seven times sealed....Never shall I forget those moments which murdered my God and my soul and turned my dreams to dust. Never shall I forget these things, even if I am condemned to live as long as God Himself. Never. 

It is this night that changes everything for him, but many awful things in this story happen during a literal night. The night before their arrival at the camp, Mrs. Schächter spends the entire train ride warning about the very thing they all find when they arrive at Auschwitz, and now it has happened. When they hangings occur, the prisoners eat the soup that "tasted of corpses" at night. Elie's father dies and is taken away in the night. 

Elie loses his innocence in this dark night of his life. He will never again be a young man as he once was; even though his ordeal in the camp does not last much longer than a year, he leaves the camp as an old man in spirit, for he has lived too hard and seen too much. He has lost his innocence by having to live through such harsh and horrific realities.

He sees so much death in this story. While every death does not impact him personally--and in fact he naturally grows rather desensitized to it--the deaths he sees are horrid. Death in the camps is an inevitability, the constant presence in his life during this time, and it seems inescapable.

Perhaps the most devastating loss for Eie is his loss of faith. We learn in the beginning of the story that Elie is not just a practicing Jew but a young man of great faith, with a sensitivity to spiritual matters. As the story  progresses, we see Elie's faith be tested and then slowly diminish--and we can hardly blame him for it. Eventually, he is unable to pray, and we understand why.

Blessed be God's name? Why, but why would I bless Him? Every fiber in me rebelled. Because He caused thousands of children to burn in His mass graves? Because he kept six crematoria working day and night, including Sabbath and the Holy Days? Because in His great might, He had created Auschwitz, Birkenau, Buna, and so many other factories of death? How could I say to Him: Blessed be Thou, Almighty, Master of the Universe, who chose us among all nations to be tortured day and night, to watch as our fathers, our mothers, our brothers, end up in the furnaces? Praised be Thy Holy Name, for having chosen us to be slaughtered on Thine altar?

To think that God does not love him is awful; to live through an experience that causes him to doubt God's promise to an entire group of people is crushing, and Elie is crushed. We know that he was a boy who prayed devoutly and with fervor; he grows into a boy who sees no reason to pray because he does not believe God will honor his prayers, if He is even listening to them. 

Just as the image of "night" is black, dark, bleak, and isolating, so is Elie's life in the concentration camp. We know that, though he is changed, Elie eventually recovers from this devastating experience and goes on to write another book entitled Dawn, symbolic of hope and a new day.