Why do you think eliezer wiszer name his novel Night?

It is a metaphor for a period in which the protagonists, Europe, and the world entered a seemingly endless darkness. They were confronted with ongoing death and destruction.

"The days were like nights, and the nights left the dregs of their darkness in our souls."

There is a pervasive despair, even at the end of the book. "From the depths of the mirror, a corpse gazed back at me. The look in his eyes, as they stared into mine, has never left me."

Note that Wiesel's memoir of this very long night of Horror was followed by his book, "Dawn", a metaphor for hope and new beginnings.