What horrible realization does Elie come to about Rabbi Eliahou and his son, and what is Elie's response to this?
Elie remembers seeing Rabbi Eliahou's son during the run through the snow from Buna to Gleiwitz. Elie remembered seeing his son run up ahead and continue running without looking back.
He knows that the son deliberately ran ahead of his father to avoid being associated with him or near him at the rear of the line. Rabbi Eliahou's son chose "life" over family loyalty. Elie sees Rabbi Eliahou's son as fickle and disloyal.
Elie promises himself that he will not behave toward his father like Rabbi Eliahou's son even if he is tempted. He does think of the extra rations he might be getting if he took from his father, but he puts this out of his mind and prays to God to give him strength and courage.
Elie proves himself to be true and loyal to the very end of his father's life.
Elie witnesses the rabbi looking for his son during the prisoners' life-threatening run/march to Gleiwitz. The rabbi is convinced that his son would never leave him and continues his search. Elie knows that Rabbi Eliahou's son saw his father stumble and become unable to keep up with the others, and he distances himself from his father. The rabbi's son chooses self-preservation over family commitment (a major theme of Night). Elie knows that he is capable of committing a similar act, and so for the first time in a very long time, he prays to God, asking Him to spare him from making the same horrendous decision about his own father.