“Alone on earth, the Church makes reason really supreme. Alone on earth, the Church affirms that God himself is bound by reason.”

This quote by Father Brown shows him arguing to Hercule Flambeau that the Church values reason. The quote thus supports The Psychological Approach to Solving Crimes, as Father Brown uses his religious faith and reason to investigate crimes, such as Flambeau’s attempted thievery of the Blue Cross. This reason has helped Father Brown get the cross to Westminster where it belongs.

“Has it never struck you that a man who does next to nothing but hear men’s real sins is not likely to be wholly unaware of human evil?”

Father Brown explains that his role as a priest grants him access to other people’s secrets. As such, he is aware of The Duality of Human Nature. This awareness of human sin allows him to solve mysteries and save souls—two complementary roles in Father Brown’s career, as the criminals he apprehends often repent and reform after speaking with him. Flambeau, the criminal-turned-detective, is the clearest example of this pattern.

“He would do anything, anything, to break what he calls the superstition of the Cross.”

Father Brown explains that Aristide Valentin, while a good and honest man for most of his life, had developed an intense distaste for organized religion and especially for the Catholic Church. This led him to experience a feeling of betrayal when fellow skeptic Brayne considered converting to Catholicism, and he murdered Brayne to prevent him from donating part of his fortune to the Church.