In Chapter 3 of Night, how has Elie changed in a short time?

In Chapter 3, Elie's father is beaten in front of his eyes, and Elie does nothing.  In a short time, Elie has learned to think of his own survival first.  He has become callous, and does not react when his own father is hurt.

While the male prisoners are waiting in a barracks with "a gypsy deportee" watching over them, Elie's father is seized with colic and politely asks the gypsy where the lavatories are.  The gypsy does not respond, except to deal Elie's father "such a clout that he (falls) to the ground, crawling back to his place on all fours".  Witnessing this, Elie does not move, not even to "(flicker) an eyelid".  He realizes,

"I had looked on and said nothing.  Yesterday I should have sunk my nails into the criminal's flesh.  Had I changed so much, then?  So quickly?"

Appalled at his own growing lack of sympathy and sensibility, Elie, after the fact, begins to feel remorseful.  He begins to understand the significance of what the Nazis have done to him; they have stripped him of his humanity, and he thinks, "I shall never forgive them for that" (Chapter 3).

Elie's awareness of how his experiences are changing him is a central theme in the book.  Although he does ultimately survive the concentration camps, at the time of his release, he is depleted both physically and to the depths of his soul.  Elie loses all the things that that are important to him and make him whom he is, and the loss is already beginning in Chapter 3.  Elie loses his faith in God and his ability to love others.