This is a great question. Here is the context.
When Elie was working in a warehouse in Buna, Poland, he worked next to a young French girl. He did not know who she was; in fact, he thought she was an Aryan, based on her looks. When the person who was in charge, Idek, beat Elie in an act of brutality and Elie was writhing in pain, the young French woman came to him and told him to hold in his anger. She also placed her hand on him and gave him a piece of bread. In short, she showed kindness. By this act, Elie thought she might have been Jewish. Later on, he says that he fortuitously bumped into her in Paris, and she told him her story. She was a Jew and falsified papers to survive.
Here is the text:
I knew she wanted to talk to me but that she was paralyzed with fear. She remained like that for some time, and then her face lit up and she said, in almost perfect German.
"Bite your lips, little brother...Don't cry. Keep your anger, your hate, for another day, for later. The day will come but not n o w ... W a i t . Clench your teeth and w a i t ... "