In the final passage of Night, Elie observes his face in the mirror for the first time since he left the ghetto. He has been liberated from the Nazi camps at long last, though he has just recuperated from weeks of illness. When he gets a look in the mirror, he describes himself as a corpse and claims, "The look in his eyes as he gazed at me has never left me." The reason Elie will be forever haunted by his reflection is because of how dramatic a change he experienced between the beginning of the war and the end of it.
At the start of the book, Elie is an innocent boy. He lives with a loving family, worships a loving God, and has faith in humankind. By the end of the book, he has lost his entire immediate family and no longer has any faith in the goodness of God or humanity. His old self died in the camps. Elie's physical resemblance to a corpse signifies both his spiritual death and how hard a toll camp life took on his physical health. That he refers to his reflection in the third person does suggest he feels a detachment from who he was in the camps as well, however, and that he will have to forge a new identity and life for himself now that he is free.