John Bunyan's The Pilgrim's Progress is an allegory, that is, he used names to represent abstract qualities. Explain how Vanity Fair, Obstinate, Pliable, Help and Faithful demonstrate the traits for which they are named, and how they affect Christian's journey.
The Pilgrim's Progress is indeed an allegory and John does use the names to express qualities in his characters.
In the story, Vanity Fair is a place where Christian (the main character who is attempting to assess his place in the world and how he should behave) is completely ridiculed. In fact, John has the people who live in Vanity Fair mock Christian and his friend and smear mud on them. Why? Because even though the people in Vanity believe that they are good people and strive for excellence, they are truly servants of Beelzebub and are trapped by their own pride.
Obstinate is just how he sounds--stubborn. When Christian first decides to leave on his adventure, Obstinate completely refuses to join him, even though he is his neighbor. This demonstrates the stubborness some people have--some sort of aversion to change of any kind. In other words, Obstinate clings to his comfortable life instead of attempting to change himself for the better.
Pliable is another neighbor of Christian's. This neighbor, instead, decides to join Christian on his journey. However, when he does join Christian, he finds himself quickly discouraged and turns back. The word pliable literally means something that bends easily--and pliable certainly does and gives up.
Help and Faithful are very different from Obstinate and Pliable. Help is another pilgrim (another Christian, if you would) who assists Christian when he falls into the Slough of Despondency. Meanwhile, Faithful joins Christian on his journey. When Christian and Faithful enter Vanity Fair (remember, Vanity is full of those who believe they are just when they are not), Faithful stands up for his faith (because he is faithful) and is then killed for his faith.