How does Mr. Tench character fit in this story, The Power and the Glory?

Mr. Tench serves as a sort of chorus in the novel, helping
to initially develop themes and providing a context for the priest
character. 

Tench is in a situation that resembles the
priest's situation. He feels forlorn and, to some extent, stranded in the southern state
of Mexico. He is cut off from his past both physically and temporally. He has known
better days and has known some measure of success. Now he is a faded and failed version
of himself. All these things are true of the priest as
well. 

Tench also introduces the priest to the story and
helps to provide exposition for the protagonist as a drinker, a man on the run and as a
frightened man. The priest's inability to save or deliver himself to safety and his
religious impotence are reflected in Tench's professional compromises. He uses sand to
form the molds he uses for false teeth: 

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"I cast in sand," Mr. Tench said. "What else can
I do in this place?"