Wiesel writes, "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."
Having seen what he saw in the camps and experienced the horrors of the Holocaust, Wiesel felt as though he would never see the light again. Night symbolizes the darkness of his oppression, imprisonment and experiences during the Holocaust.
The trilogy is amazing and Nightis only one small part of it. I think that the title came from Elie's experience in the concentration camps. Before he gets to the camps and after the Germans have invaded Sighet he feels that night is the only safe place for him because nothing happens at night. When he gets to Birkenau he learns that first night, that night no longer holds safety for him. He says that the first night in camp changed his entire life. That night he says his life "became one long night seven times sealed". He is talking about how a dark shroud fell over his life at that point and it never really lifted because he would never forget the things he faced that first night and every night after that for the next year. At fifteen years old he faced his own mortality- burn alive or throw himself onto an electrified barbed wire fence. He lost his mother and sisters without getting to say goodbye. He lost his faith, his childhood, his illusions.
Psalm 30:5 says: "Weeping may endure for a night,/ But joy comes in the morning."
Wiesel doesn't really say why he titled his book Night. My edition has a Preface written by Francois Mauriac. Wiesel has recently published a new translation and has written a new Preface himself. He may make some mention in it of why he chose this title.
It could be that, for Wiesel and his family, the long nightmare of the Holocaust began at night. The eNotes introduction states: "The metaphorical night only gets darker as Eliezer struggles to survive in the brutality and degradation of the camps."
The original title was "And the World Remained Silent," but Night evokes the fear and sense of unreality--even surreality--of Wiesel's experiences. You might be interested in knowing that Night is book one of a trilogy, with Dawn and Day completing it.