In the beginning part you are referring to they are being transported from one ghetto area to another. Wiesel says:
The barbed wire which fenced us in did not cause us any real fear. We even thought ourselves rather well off; we were entirely self-contained. A little Jewish republic ... We appointed a Jewish Council, a Jewish police, an office for social assistance, a labor committee, a hygiene department—a whole government machinery. Everyone marveled at it. We should no longer have before our eyes those hostile faces, those hate-laden stares. Our fear and anguish were at an end. We were living among Jews, among brothers ... It was neither German nor Jew who ruled the ghetto—it was illusion
The significance of this part is that they (Jewish) people were willing to believe in an illusion at this point. Wiesel is, in part, saying in the book, Night, that many people in Europe at that time, including some of the Jewish people, were too willing to believe in an illusion.
The mood here is suspicion. He speaks about his brothers or fellow Jews and of being together in a community and having a self-contained society. However, the tone or mood is suspicion and mistrust. It doesn't make the reader feel relaxed, but it makes the reader feel like somehting bad will come, like a calm before a storm.