In Night by Elie Wiesel, what does this figurative language refer to: "...as would a shopkeeper receiving a delivery of old rags"?

The quote from Night by Elie Wiesel you refer to in your question is found on page 47 of the book. At this time, Elie, his father, and several others of the Jewish prisoners have recently arrived at the concentration camp, Buna. They have been assigned to work at a warehouse making electrical fittings. Elie meets a musician named Juliek who tells him about the work they will do, which he describes as being fairly easy and "not dangerous" (Wiesel 47). When the group arrives at the warehouse, they are met by the man in charge, the meister. Elie observes his lack of interest in them when he says,

"He paid about as much attention as a dealer might who was just receiving a delivery of old rags" (Wiesel 47).

In other words, that was all these Jewish workers were to him. They had no meaning to him as human beings. They were to be used and thrown away—totally expendable, like a pile of rags.