Eliezer's father survives selection because of Eliezer. Eliezer's father was slated for selection. Yet, Eliezer is able to inch his way through the lines and bring him back to the "right" one. In this, Wiesel shows how much survival was based so much on the sense of the arbitrary and pure "luck," if one wanted to call it that:
I inched my way through the crowd. Several SS men rushed to find me, creating such confusion that a number of people were able to switch over to the right- among them my father and I. Still, there were gunshots and some dead.
In this confusion, Eliezer was able to retrieve his father from the selection of Gleiwitz and forced to leave the camp on to Buchenwald, where the father will die. In the end, there was no overarching or transcendental reason why the father survived selection. Eliezer's grasp of the situation as well as the "luck" that other prisoners were switching lines became the critical reason why the father lived and others did not.