The correct answer to this open question is the following.
Eliezer's journey in faith is a major area of focus in the novel.
The state of Wiesel's faith at the beginning of the book is high and very important to him to overcome the situation. He worshiped God all the time because that was what his father taught him to do and he firmly believed so. He said "Why did I pray? Why did I live?" To show that he had blind faith in God.
However, as the story goes on and Eliezer realizes the horror of the concentration camps, the injustices he witnessed, and all the pain and suffering from the people, he started to have doubts. Indeed, big doubts and many questions.
That is why at the end of the novel, his faith is different. He questions himself "How a benevolent God can allow those atrocities?"