I get the sense that Elie has a clear understanding of those dark aspects of his life which were revealed to him during his time in the camps.  He knows what he was when he started, a sincere seeker of God.  He knows what he became in the camps, a young man who had lost his faith both in God and in man.  He knows what he almost became, a man who nearly became an animal and disowned his own father.  He knows those things and he must face them.  Remember he wrote this ten years after the experience, so he does see with new eyes and from the vantage point of time.  Even so, he knows what he nearly became and what he nearly lost--his faith in God and man.

I think one of the clear messages of the novel is how, when we are treated inhumanely, we come to treat others inhumanely as well. This is something that Elie is forced to confront in himself when at times he feels anger towards his father and their relationship is threatened as a result. Consider the first time Idek attacks Elie's father. Elie's immediate reaction is to feel annoyed at his father for drawing Idek's attention. This is one example of how the narrator is forced to confront the darkness within himself, even though he struggles against it throughout the novel.

I think that the quote you have identified fits your assignment, but your interpretation is slightly flawed.  When Elie first enters the camp and witnesses infants being thrown in to the fire, he vows that he will never forget that night because that is the night that he loses his faith.  During the chapters between his first experience in the camp and the near-miss selection with his father, Elie becomes increasingly resistant to faith or the idea of a caring God.

However, when his father returns safely from selection, Elie demonstrates that he still has a little faith in intangible elements such as miracles and also realizes that even though sometimes he viewed his father as a burden, he is extremely relieved that to see his father again.