When Elie Wiesel looks into a mirror for the first time in a year, what does he see gazing back at him? Why is this important?

Eliezer see a corpse looking back at him. The vision he stares at in the mirror unrecognizable to him: "From the depths of the mirror, a corpse gazed back at me. The look in his eyes, as they stared into mine, has never left me."