Well, in this richly allegorical work of fiction, some of the main themes are suggested through the motif of the journey and the pilgrim. Characters seem to be defined by their pilgrim nature or their lack of it in the text. Consider the main characters that we are presented with who are travelling towards the Celestial City. Christian, Christiana, Faithful and Hopeful are all journeying towards this goal and their character is revealed by their intent to reach the city. However, on their way, they encounter a large number of other characters who again show themselves for who they are by their intention to reach the Celestial City or their decision to stay where they are and keep them away from the Celestial City. Again, as with all the characters, names are incredibly significant in suggesting the various traits of characters. Prejudice, Ill-will and Obstinate, for example, make clear their opposition to the Celestial City and what it represents.
Thus we can see that the key theme of the journey and how characters respond to this theme defines them and reveals a lot about their character as we are presented with a world where everyone is judged based on their attitude to this pilgrim adventure