How do Mr. Bingley and Jane Bennett in Jane Austen's, Pride and Prejudice, help illuminate the relationship between Mr. Darcy and Elizabeth Bennett?
I just need help forming some sort of idea about how a pair of characters can highlight the central characters in a piece of work.
The relationship between Mr. Bingley and Jane Bennet in Jane Austen's novel Pride and Prejudice is meant to represent an inverse reflection (known as a foil) of the dynamics that take place between Darcy and Elizabeth. A foil, in literature, is defined as any sub-character (or secondary character) that is used to contrast the main character (or an idea meant to contrast the main idea).
You asked how a (secondary) pair of characters help highlight the main characters of the story. The answer is that Austen, and many other authors, utilize the foil technique as a way to allow the reader to contrast the two situations and, in an sort of interactive way, come up with solutions, conclusions, and comparisons that may help solve the central problem of the story.
In all, these techniques are also effective in establishing a strong bond between the reader and the author. It always works well. Therefore, to concisely answer your question, the way in which one character highlights another is by foiling it.
To illustrate this explanation, think of how Jane and Bingley seem to be quite alike: Both are a bit shy, sympathetic to everybody, and none of them have the gall to take the first step in declaring love for each other. In fact, their relationship is so passive that even Charlotte Lucas wonders when "anything official" would take place. Similarly, Mr. Bennet judges them to be so complaisant with everything that he feared that they will end up failing in the financial sector. What Mr. Bennet basically declares is that, to him, Jane and Bingley are so alike (and sort of airheaded) that he worries about them.
In a huge contrast, we find Austen clearly focusing on the relationship between Darcy and Lizzie. They are both passionate and sort of enigmatic. He is proud, aristocratic, and prude. She is prejudiced, independent, and an outspoken smart-mouthed girl. Both hate each other, both love each other, both get confused with each other....it is a roller coaster with Darcy and Elizabeth. And, yet, everything gets fixed happily in the end.
However, it would have not been as effective to show the one sided aspect of Darcy and Elizabeth without first presenting us with the story of Jane and Bingley. Just as we have had enough glurge with those two, the action begins: We see the darker side of the love moon in Lizzy and Darcy.
Conclusively, the use of a foul to highlight the unique characteristics of the main character of a story is an effective method to bring the reader closer to the main character. It allows the reader to compare, contrast, and create connections to the story. That is always a positive thing in literature.