[Chapter 3] as the intended victims recite the Kaddish the prayer for the dead, the narrator feels a revolt against God, why does he feel this way?

Elie can't handle praying to a God that would let this happen to his own people. Eliezer says he will never forget that night and the children's faces that he saw burned in flames. On that night his faith was consumed, and the silence of the night made him lose his will to live.