Let us focus on what happens in this scene. It is clear from the way that Jenny catches Willy talking and arguing with himself that Willy is retreating more into his make-believe world of fantasy as a defence mechanism against being fired. What he cannot stand, and what he partially admits in the scene with Bernard, is that Bernard has made a success of himself and that Biff, Bernard's childhood friend, has not. Even though Bernard was so weedy and weak as a child, it is he who has done well in life, and has a very god job, prospects, a wife and two kids. Initially he clings on to the illusion that Biff is "working on a very big deal," but then he abandons this lie to ask what happened and "what's the secret" of Bernard's success. Bernard explains that Biff's downfall began after he went to visit Willy in New England, which tells Willy that Biff found out about his affair.
As if to really rub Biff's failure in life in, as Bernard goes and his proud father looks on, Charley reveals that Bernard is going to argue a case in the Supreme Court. Willy is stunned, as he can't believe that Bernard never mentioned such an achievement. Charley's response cements the difference between the two families and how they live their lives:
He don't have to--he's gonna do it.
This of course is highly significant. Willy and his boys are always talking about their new plans and dreams to achieve success. In contrast, Bernard and Charley do not talk about achieving success--they go out there and achieve it.
Thus this scene seems to present us with an increasingly unravelling Willy and also to reinforce the failure of his own and his childrens' lives.