Bernard is again contrasted with Biff. What is the effect of doing this?

Bernard used to be a nerd and a great admirer of Biff's athletic achievements in High School. Now Bernard is much more, in the eyes of Willy, successful. This really makes Biff feel badly about himself. Willy is unknowingly shaping his own son into a version of himself. By cutting Biff down, Willy is destroying Biff's identity and self-esteem.