How do Obstinate and Faithful show the traits they're named for, and how do they affect Christian's journey in the allegory The Pilgrim's Progress?
Obstinate, and other characters like him such as Pliable and Vanity Fair, demonstrate the negative meaning of the words that are their names by the way they think and behave. Other characters, such as Help, Hopeful, and Faithful, demonstrate the positive meanings of the words that are their names also by the way they think and behave. To illustrate the point through Obstinate, When Christian is running from the City of Destruction where he was born and had a wife and children ("the man ... ran on, crying, Life! life! eternal life!"), his neighbors come out to watch him run ("The neighbours also came out to see him run"). One among them is his neighbor Obstinate, who chases after Christian to try to stop him and force him to come back (Pliable goes in pursuit with him).
His obstinacy is shown when he not only rejects what Christian is saying--because after all, Christian doesn't really offer much of an explanation--he goes further and calls Christian a "coxcomb" (a proud and vain man) who considers himself "wiser in his own eyes than ... seven men" put together. In effect, Obstinate is accusing Christian of being obstinate and proud and unreasonable. Ironic, isn't it? The affect Obstinate has upon Christian's journey is not to speak of: Christian continues onward, going toward where the Evangelist directed him--but he has a new companion to the city gate because Pliable--true to his name--has been convinced (a bit too readily without much benefit from applying rational thought) to believe Christian and go with him on his run for the gate.
Faithful was meant to have gone with Christian from the start but Christian got it into his head to start out without him, nonetheless, true to his name, Faithful went on his pilgrimage steadfastly. When Christian and Faithful finally come abreast of each other after the Valley of Humiliation--who though starting second, got ahead of Christian because he was not waylaid and side tracked--Faithful affects Christian's journey by giving him good companionship and a fresh view of the journey as they share the stories of their adventures together. In addition, Faithful's discourse provides Christian with sound theological and doctrinal instruction as he tells what he said to tempters like Shame and Discontent:
Faithful: Yes, I met with one Discontent, who would willingly have persuaded me to go back again with him; ... I told him, ... he had quite misrepresented the thing; for before honour is humility, and a haughty spirit before a fall.