Whats the most important quote from chapter 9? Why?

This really depends on what you see as important. I can pick one but that's just my opinion.

"After my father's death, nothing could touch me any more." Chapter 9, pg. 107

I think this really shows Elie shutting himself off. After his father dies, there is really nothing left that the Nazis can take from Elie. At this point, Elie isn't even concerned with his own life or belief in God.