One of the most resounding lessons to emerge from Wiesel's work is the idea that individuals must always speak out against aggression and the denial of individual rights. The narrative offered is so powerfully horrific that the conclusion of the work makes it a moral, ethical, and political reality which demands speaking out against any order which takes away human rights and dignity. In examining the setting which denies bonds between families and human beings, one cannot be helped but speak out against such injustice. One positive lesson from the work is that anything which could be remotely similar to what Eliezer experienced has to be struck down immediately.
One positive lesson is that the Holocaust allowed some people to value their family more than they did before deportation. Elie's relationship with his father is not the best is could be. His father sees him as an immature boy, and Elie sees his father as oblivious to what is happening around him. By the end of the book, Elie has taken responsibility for his father and most certainly is closer to him before their camp experience.
Another positive lesson is that Elie gains an immense amount of self-knowledge during the Holocaust. He learns what he is capable of and that exacting revenge (such as the freed prisoners immediately hunting down their oppressors) doesn't usually help someone heal from a horrific experience.
While Elie learns some valuable lessons from being a Holocaust victim, one must still argue that those lessons could have been learned without his having to endure such awful circumstances.