In Death of a Salesman, what are the dramatic changes in the life of Bernard over the years in which the play is set?

Bernard is used as a foil to compare his success to the
dismal failure of Biff and Happy's lives, which of course is indirectly a comment on
Willy Loman's failure as a father to bring up his children. Bernard is the son of
Charley, who in the play is Willy's only friend and someone who tries to help him.
Bernard was always mocked by Willy as a child, as he was studious and hardworking, but
not good at sports in the same way that Biff and Happy were. Thus he was an object of
scorn for Willy, who thought he wasn't "manly" enough. However, as an adult, he has
worked hard to become a very good attorney, and is even going to argue a case in front
of the Supreme Court. He stands as a living rebuke to Willy for the way in which Bernard
has achieved the success to which his own boys have always worked towards but never
managed to gain. Perhaps one of the most telling remarks that offers a subtle commentary
on the differences between Charley and his son and Willy and his boys is that when Willy
remarks that Bernard didn't mention about his case in front of the Supreme Court,
Charley says:

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He don't have to--he's gonna do
it.

This of course contrasts
quiet, purposeful action with the endless, impractical dreaming of Willy and his boys,
that never gets further than mere speech.

Thus Bernard
represents a character who has quietly but diligently worked at making a success of
himself, and has succeeded. His purpose is as a foil to Biff and Happy, who, like their
father, have not achieved their dreams.