The answer is: the rationale for the Holocaust will always be incomprehensible.
In the excerpt from "All Rivers Run to the Sea," the author Elie Wiesel expresses his inability to understand why the horrors of the Holocaust happened. He mentions he did not understand and neither did survivors. He wonders about the people who died, especially in Birkenau, which was part of Auschwitz concentration camp and which he calls "death factory."