Moshe the Beadle, in the story called "Night," is Elie Wiesel's spiritual adviser in his Jewish faith. Despite the fact that Moshe disappears after the first few pages of the book, the ideas he teaches Elie resonate throughout the rest of the story and throughout Elie's life.
Moshe studies and shares his views with Elie about Jewish mysticism. He is Elie's Cabbala teacher and talks about the riddles of the universe and god's importance in the quest for understanding. With Moshe's teachings, even after Moshe is no longer in the book, Elie questions his faith, which is part of the Jewish mysticism. This continues until Elie witnesses the death of the pipel in Buna. At this point, Elie becomes full of answers, not questions. It is at this point that Elie loses his faith.
Another reason Moshe is so important to Elie is because of the warning Moshe gives to the people of Sighet before they are put into concentration camps. Moshe considers himself a messenger after escaping the Gestapo in Poland. However, his behavior leads the Jews to believe he has lost his mind and they ignore the warning. This knowledge is something that Elie takes with him throughout his journey through the concentration camps.