To put it simply, an idealist is one who imagines that the world can be a much better place than it is. What could be dangerous about that? The lieutenant, in many ways, illustrates the danger. Obsessed with the way things could be, he remains mired in dissatisfaction and bitterness about the way things actually are. Although the wish to help the poor is a noble sentiment, dreams of "starting over", erasing history, and wiping out all religious belief are simply not realizable. Moreover, being unable to bring about the impossible leads the lieutenant to feelings of frustration and anger, an even more keen awareness of how imperfect the world is, and hatred for those people whom he views as obstacles to the realization of his dream. Moreover, his conviction that he knows what is best for the people is itself a form of arrogance. The priest, on the other hand, comes to accept suffering and death as a part of life; that is not to say that he does not wish to help alleviate suffering, but his faith in the next world helps him to accept the trials and hardships of this one.
Greene is interested in showing the gap between life as it is remembered, recorded or retold, and life as it is lived. Acts of storytelling occur quite frequently throughout the novel. The most obvious example is the story of Juan, the young martyr. One thing that becomes apparent by the novel's close is how very different Juan's story of martyrdom is from the priest's. Juan's life is characterized from start to finish by composure, loyalty and, above all, unshakeable faith. Although the priest certainly is an admirable figure, especially by the time of the novel's close, he still faces death afraid and unable to repent. But Greene is not juxtaposing the two accounts of martyrdom merely to highlight the priest's shortcomings, but rather to show that real-life differs from idealistic stories, in most cases. This theme extends beyond storytelling to other forms of representation. For example, the priest takes note of how little the gringo looks like his picture on the wanted poster in the police office, and the lieutenant fails to recognize the priest because the priest does not have the delicate hands that a stereotypical priest would have. Stories, pictures and other kinds of representation can give a misleading, exaggerated picture of a person, and Greene is interested in writing about reality as it is truly experienced, even if he himself is attempting to create that sense of unvarnished reality through his own storytelling.
Love and hate, beauty and suffering, good and evil are just a few of the many pairs of seeming opposites that Greene insists are not really opposites at all. In the lieutenant's case, for example, his hatred of priests originally stems from a love of and a concern for poor people. Both feelings stem from the same strong emotions—the desire to protect the innocent and the rejection of injustice in any form. The priest often discovers the beauty of life in the moments of greatest suffering and hardship. Moreover, the priest and the lieutenant, who play such opposing roles throughout the novel (i.e. the hunted and hunter, the priest-hater and the priest) come together at the end of the novel and reach a kind of qualified understanding of one another.
One of the most knotty problems considered in this book is how difficult it is for a Christian to be truly humble. Humility is a quality that a Christian is supposed to strive to realize in his life; yet as soon that person thinks that he is succeeding in being humble, he can become proud of his success. The priest realizes that he is trapped in this quagmire, and that he originally stayed in Mexico during the persecution so that he would appear good before God and his people. Yet, in the novel, he never allows himself to remain complacent in the sacrifices he has made, or the Christian feelings he has. Despairing over his weakness and inability to be truly humble, the priest, paradoxically, attains true humility.