"Then I remembered something else, his son had seen him losing around, limping, staggering back to the rear of the column. He had seen him. And he had continued to run on in front, letting the distance between them grow greater. A terrible thought loomed up in my mind . . ." What does Elie mean by this?

In chapter six, Elie and the other Jewish prisoners are exhausted from their overnight journey in the snow, and they must cram into a tightly packed warehouse. When Rabbi Eliahu enters the shed, he is looking for his son and asks Elie if he has seen him. Rabbi Eliahu proceeds to say that he lost his son during the march because he did not have enough strength to keep up the pace. Elie responds by telling the rabbi that he did not see his son, and Rabbi Eliahu leaves the shed. Moments after Rabbi Eliahu leaves, Elie recalls witnessing his son during the march. Elie remembers seeing the rabbi's son purposely march at a faster pace in order to distance himself from his father. Rabbi Eliahu's son could feel his father becoming weaker and purposely quickened his pace with the hopes of leaving his father behind and unloading his burden. The terrible thought that crosses Elie's mind is that Rabbi Eliahu's son wanted his father left behind to die in order to make his own life easier. Elie sympathizes with Rabbi Eliahu's son and begs the Lord to never allow him to abandon his father like the rabbi's son.