what are the words that have any meaning to wiesel? why would he feel this way?

From the text:

CONVINCED THAT THIS PERIOD in history would be judged one day, I knew that I must bear witness. I also knew that, while I had many things to say, I did not have the words to say them. Painfully aware of my limitations, I watched helplessly as language became an obstacle. It became clear that it would be necessary to invent a new language. But how was one to rehabilitate and transform words betrayed and perverted by the enemy? Hunger—thirst—fear—transport—selection—fire—chimney: these words all have intrinsic meaning, but in those times, they meant something else.

During the time period he wrote Night, Wiesel understood that many of the words he used held a different meaning for us than they did for him. Words like hunger and thirst may have been the first that came to his mind, but he also knew that the average reader (you and I) could never comprehend the true meaning of those words.