opium of the poor

I don't know weather we can call it an "opium" for the masses. That's a pretty general statement. Religion certainly plays a big part in this novel. Although people misuse religion, it also has its place in culture and tradition. 

Papa uses his faith to justify abusing his children. Religion alone is not to blame. Papa represents the wave of fundamentalism in Nigeria that corrupts faith. Father Amadi, on the other hand, is an African priest who blends Catholicism with Igbo traditions. He believes that faith is both simpler and more complex than what Father Benedict preaches. Father Amadi is a modern African man who is culturally-conscious but influenced by the colonial history of his country. He is not a moral absolutist like Papa and his God. Religion, when wielded by someone gentle, can be a positive force, as it is in Kambili’s life. You can check out more at the GradeSaver link below.