The portrayal of Christianity in "The Second Nun's Tale" focuses on revealing how this faith differs from the pagan one it replaces. Cecilia promises heightened senses to Christian converts, a chance to see things invisible to the naked eye. This heightened vision contrasts with the blindness of a pagan like Almachius, who cannot even see that his idols are made of stone. This heightened vision is probably symbolic of the amped-up philosophical and spiritual smarts a Christian has just because he's a Christian. Another way in which Cecilia distinguishes Christianity from Paganism is in its access to a living God – living because God was born and walked on the earth among humans in the person of Jesus, but also living in the promise of another, eternal life after this earthly one. The pagan god, by contrast, is dead, says Cecilia. The speechlessness and deafness of those stone idols comes to symbolize their lack of access to the eternal life Cecilia's faith promises its followers.
"The Second Nun's Tale" uses the dumb and deaf idols of the pagans to symbolize the lack of eternal life in the pagan faith.
"The Second Nun's Tale" is most concerned with God's status as a "living" God.