Paul's journey from Catholicism to atheism mirrors his coming of age and his disillusionment with American society and capitalism. The Catholic Church is not described as a compassionate institution that helps the immigrants' community, but as detached and oblivious to their needs. Thus, together with Job and the Boss, the Church functions to keep immigrant workers in their own marginalized place. The text personifies the work as a bricklayer that Paul is forced to take up at the death of his father in the material god Job. The narrative draws several parallels that make readers associate this material god to the spiritual one of the Catholic Church. Capitalism and Catholocism are seen as supporting one another and as conniving in the exploitation of workers. Thus, Paul's rejection of the Catholic Church implies that he is no more willing to be exploited by others. Commentators of the novel such as Fred Gardaphè and Maria Paola Malva (see second link below) point out that, by rejecting Catholicism and Capitalism, Paul is becoming "his own God" and is taking his own fate in his hands.
This text is above all one of protest against a system that seems implacably opposed against those most in need, and one where the church and religion is inextricably intertwined with politics and power. Let us remember that the story gives us insight into the world of Italian immigrants in America, who are only able to work as construction workers, facing incredible dangers every day. What helps them make it through each day is their strong faith in Catholicism and the idea that they are working so hard to spare their children similar difficulties.
The crushing, painful and torturous death that the construction workers on Geremio's team suffer symbolises the kind of sacrifice that the American Dream demands from those who seek wealth and fortune in America. As the building begins to collapse around them, the American Dream quite clearly becomes some kind of twisted nightmare, And Geremio's moment of epiphany before he dies in a way that mimics Christ's death forces him to realise the way that he has been systematically cheated throughout his life by those in power.
What is so key about Paul's conversion to atheism therefore is that he has learnt the lesson that his father only learnt moments before his death. Paul recognises the tremendous irony in his father's death and the comparison with Christ's death. Jesus of course died for a specific purpose and managed to save mankind as a result. As Paul stands beside his father's grave, he sees that Geremio's death on Good Friday, the day of Jesus' death, is a meaningless sacrifice that is the direct result of the unfeeling nature of men whose treatment of immigrants as nothing more than cheap labour "justifies" such sacrifices. Paul's adoption of atheism therefore represents his resistance of the forces and ideologies that have so successfully trapped his parents and immigrants as a whole.