In Chapter 3 of "Night," when questioned by the S.S. officer, why did Elie lie about his age and occupation?
As mentioned above, Elie lies about his age and occupation so that he can stay alive for as long as possible. A kind prisoner advises both Elie and Shlomo to be wary about admitting the truth before the S.S. officers; telling the officers how old or how young one truly is can result in immediate death.
This is because prisoners who are too young, too old, or too infirm are considered unfit for manual labor. Historical documents show that many babies, pregnant women, and the handicapped were not spared by the Nazis; on arrival, they were told that they would be taking showers, unaware that, once in the 'showers,' carbon monoxide or Zyklon B pellets (an extremely poisonous insecticide) would be released into the air shafts.
In the novel, the prisoner advises Elie to say that he is eighteen years old (rather than fifteen) so that he can be considered a viable candidate for work detail. Elie is also instructed to lie about his father's age and to claim that Shlomo is forty years old instead of fifty. At the entrance to the camp in Auschwitz, there is actually a sign that reads 'ARBEIT MACHT FREI' which means that 'work makes one free.' However, this is an euphemistic phrase describing the Nazi method to exterminate whole groups of people through slave labor.
Elie also lies to the German officer about his profession; he claims to be a farmer. Since farmers are known to be used to manual labor, the guard lets Elie pass without much argument. During the war, the camp at Auschwitz was especially known for forcing prisoners to perform backbreaking labor on behalf of the Nazi war effort. Many had to work in rock quarries, in coal mines, on construction projects, and in factories. Others were forced to clear rubble and debris off the roads after an Allied attack. Between the crematorium and slave factories, millions of people were killed in Auschwitz during the war.
In the third section of Night, Elie and his father have just arrived at Auschwitz. They are told by another prisoner that Elie needs to lie about his age. He needs to say he is eighteen and his father needs to say he is forty. This will give them the greatest chance of survival. If the SS officers see that the two men can work, then they will keep them around instead of killing them right away.
Elie tells the guards he is eighteen and a farmer. He thinks that if the officers think he has worked manual labor, then his chances are better. Elie and his father are chosen for work detail and are kept together. Elie is happy that he gets to stay with his father. He thinks he can watch out for him and keep him safe. At this point they still are not sure of where they are or what goes on here. As they start marching they pass a ditch were babies are being burned alive, then pass another ditch where adult bodies are being thrown. The men break down in tears. Elie feels a sense of where they are. He knows that his and his father's lives are in danger.
This is the first time we see Elie start to question his faith. He just doesn't comprehend how God could allow these things to happen. He vows to never forget, and he teaches us, through his terrible tragic nightmare, that we are to never forget as well. If we do forget, it is bound to happen again.
Elie knows that if he gives his true age he will be considered too young to be able to stay with his father. He will probably be marched off to the gas chamber. He also knows that he needs to find some reason the Nazis will find him useful. So, he lies about his occupation so that the Nazis will decide not to kill him but to send him someplace where they can use his skills.