How important is religion to the way Eliezer defines his identity?

That
religion is a central element in Eliezer's life is obvious from the opening pages of .
This is before war and genocide have impacted the people of his hometown, Sighet.
Eliezer is interested almost to the point of obsession in finding a teacher to instruct him in
Kabbalah. It's not a case of his being expected to become a scholar of the Jewish writings; in
fact, it's almost the opposite, because his father tries actively to discourage
him from pursuing this activity. "There are no Kabbalists in Sighet," his
father tells him. Altogether, it is a basically secular family and a secular community in which
young Eliezer finds himself. This fact in itself makes his own interest in religion even more
significant than it would have been had it simply been the normal thing to do for the Jewish
population of Sighet.

The one person Eliezer bonds with, especially over the
issue of religion, is Moishe the Beadle, who is the closest he can find to a Kabbalist and a man
who can help him with his religious studies. It's significant, and ironic in a grim sense, that
Moishe is the only one who attempts to warn the Jews about the danger they're in. Because he's a
foreigner, Moishe has been deported before the others and has seen the mass murder of the Jews
taking place. He has escaped and managed to return to Sighet, but no one believes his story. It
is perhaps emblematic of the whole issue of denialthe refusal of the Jews who have not yet
experienced it to believe that such things could possibly be happening, and will in fact happen
to themthat it is a religious man who learns the truth first and tries to
warn them. Their refusal to believe him is a counterpart, in some way, to their secularism,
their embracing of modernity, and their overall incredulity that such savagery could be taking
place in the modern age.

Once in the concentration camp, Eliezer's religious
beliefs are shaken. Like others, he cannot grasp why God would allow these things to happen, but
he repeatedly tries to contextualize the atrocities in terms of the teachings of Judaism. Men
are reciting Kaddish, the prayer for the dead, and he observes,

I don't know whether, during the history of the Jewish people, men have ever before
recited Kaddish for themselves.

It is not surprising that
the victims, under these circumstances, would be completely shaken in their faith. But Eliezer
repeatedly asks why? again and again. His identity as a religious person is
so strong that, although his faith is shaken, he cannot abandon the thought
of God and his bafflement that God would allow this massive atrocity to take place. But at the
end of this "journey," after his father is gone and the camps have been liberated,
there is no longer any mention of God. Eliezer finally is able to look at himself in a mirror,
and he describes what he sees as a corpse staring back at him. Finally, his religious belief has
been purged from him, and even if it has not been, his recognition that he has become one of the
living dead overrides whatever remains of his thoughts of God.