In Jewish customs, the number seven is a very important number. It number represents purification and mourning. The number seven is the symbol for all association with God, and they see the number seven as the Divine number of completion. Elie Weisel's Night is the account of his time in Auschwitz during the Holocaust. As a young boy, Elie studied the Torah and became interested in the Kabbalah, which is Jewish mysticism. Being sealed is a big part of the Kabbalah teachings. You have to be sealed to move on to the next spiritual plain to reach God. A soul must be sealed to get through the seven gates on the journey.
In Night, we see Elie go through his own spiritual journey, one of faith to one of losing his faith to the horror he witnessed. Elie and his father have survived the first night and Elie realizes what the smoke he saw really is. He doesn't know how God could allow these things to happen. He questions everything he once believed. The journey that he goes through is a heart wrenching one. He writes about the things he will never forget during his time there.
"Never shall I forget that night, the first night in camp, which has turned my life into one long night, seven times cursed and seven times sealed. Never shall I forget smoke. Never shall I forget the little faces of the children, whose bodies I saw turned into wreaths of smoke beneath a silent blue sky. Never shall I forget those flames which consumed my faith forever. Never shall I forget that nocturnal silence which deprived me, for all eternity, of the desire to live. Never shall I forget those moments which murdered my God and my soul and turned my dreams to dust. Never shall I forget these things even if I am condemned to live as long as God Himself. Never."