What is the primary lesson that Elie Wiesel teaches us in Night?

Elie Wiesel's Night is a haunting tale of 15-year-old Eliezer's experience with his father in the Auschwitz, Buchenwald, and Buna death camps, which were operated to control and kill Jewish people under the Nazis' oppressive regime during World War II. It can be argued there are two primary lessons Wiesel relates to the readers of Night: One is about always remembering the atrocities of the death camp. The second is about the delicate nature of faith in God when one experiences evil committed by humanity, and how questioning a god is often central to faith itself.
Eliezer witnesses things that haunt him and shake him to his core. Throughout the book, he repeats the phrase "never shall I forget" when recounting horrible experiences he has: his first night there, the corpses of innocent Jewish people in ovens, the internal silence that he experiences inside himself, and the abhorrent behaviors he sees in the people around him. It becomes most important that he—and all of us—remember this horrible time in human history.His faith in God is shaken by these atrocities. Before his experiences in the death camps, Eliezer views faith the same way he views breathing: it is an intrinsic part of his life, and God is all around him. But watching the horrible things that go on around him (committed by the Nazis and by fellow Jewish prisoners desperate to survive) makes him question how a benevolent god could be responsible for such evil. Through this narrative, a message rings clear about how easily one's faith can be challenged. Eliezer questions God in chapter three:

"Why should I sanctify His name? The Almighty, the eternal and terrible Master of the Universe, chose to be silent. What was there to thank Him for?"

The questioning of God's plan and God's presence is something Eliezer does throughout the story, and something Wiesel suggests is a part of any faithful person's journey.The story Night helps us to understand existential questions of faith and memory through the backdrop of one man's experience in a true-life horror story.