Why are the scenes with Willy's brother Ben necessary to explain Willy's point of view in "Death of a Salesman"?
These scenes are necessary to understand Willy because it gives the reader a glimpse into Willy's past, and all the events that led to his development of such a complex, mysterious, and odd personality once it was his turn to be the head of a family.
Ben appears in Willy's memories, particularly when Willy is hitting his lowest points and feels suicidal. Ben found success in Africa, and became all that Willy could not be. Willy was actually abandoned by Ben when he was four years old when Willy's father had, in turn, abandoned his family. The fact that Ben left the family in search of the father and ended up finding fortune plays an important pattern in Willy's own life: He too abandoned his family psychologically, but he found no fortune. His number was not the lucky number.
Hence, Ben accentuates the feeling of despair and lack of control over life that Willy was experiencing. Also, Ben is the antithesis of Willy: He was his positive opposite. This is greatly important for the sense of self in Willy's character.