Discuss the significance of the physical setting in The Poor Christ of Bomba.

The physical setting of The Poor Christ of Bomba is split between two "realms." There is the supposedly Christian realm of Bomba, the missionary city, and the pagan realms of the jungle and villages of the Talas. The town of Bomba itself acts as a refuge for Christians, a symbolic city on a hill that is supposed to be a light in the darkness to the outlying villages.
The priest, Father Le Guen, believes that the people of the city are proper Christians. However, they are deceiving him. It is only when he ventures out into the villages seeking to baptize the Talas that the frail nature of the church in Bomba comes to light. On his tour, Father Le Guen finds that many of the churches he constructed for the villagers are rotten and falling—a symbol of both the spiritual resistance of the Talas but also the ineffective nature of his mission in the country.
It is ironic but also telling that it is through the journey to the heathen villages that he starts to understand the fruitlessness of his twenty-two years working among these people. He begins to see that not only can he not reach the Talas in the outlying villages, but the entire city of Bomba and his convent for Christian wives is a facade.
The town of Bomba is symbolic of the failures of colonialism. Despite the veneer of Christianization, the people of Bomba are really after the material fruits of colonialism—they don't want God, except as a means to make money. In the same way, colonialism's aims to convert the colonized and change their culture is ultimately fruitless.
That is why, despite all the "progress" Father Le Guen thinks he made earlier in the story once he leaves the city, it disintegrates into a crumbling ghost town. Once the colonizers go, many of the structures, ideas, and systems they establish fall by the wayside—never genuinely adopted by the people they colonized.