To what extent does religion become important in Roy's The God of Small Things?

Kerala, the setting of the novel, is one of the oldest
Christian regions in the world.  Since much of Roy's focus is showing the contradictory
forces at work in the area, religion plays significantly into the paradoxical
combination of forces at work.  Roy is most obviously criticizing the caste system,
which is at odds with both Christianity and communism.  Ammu's family is for the most
part Catholic, but they honor the caste system that treats paravans as subhumans, who
should walk backwards so that they can sweep their footprints
away.

Roy explains why the Communist party was successful
in the Christian populated Kerala.

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There were several competing theories.  One was
that it had to do with the large population of Christians in the state . .
.Structurally--the argument went--Marxism was a smple substitute for Christianity. 
Replace God with Marx, Satan with the bourgeouisie, Heaven with a classless society, the
Church with the party, and the form and purpose of the journey remained
similar.

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The trouble with this theory was that in Kerala
the Syrian Christians were, by and large, the wealthy, estate-owning (pickle
factory-running), feudal lords, for whom communism represented a fate worse than
death.

Roy goes on to explain
a better theory:  as long as communism did not upset the traditional caste system, it
was allowed into the region.  Both communism and Christianity were tolerant of the caste
system.  We see throughout the novel that Christians and communism are both part of the
machine that ultimately crushes Velutha, the Untouchable.