Futility
Scobie's life pulls him along on a path from which he cannot seem to deviate. At the beginning of the novel, he appears content with his mundane life in the colony and does not particularly care about advancing; he notices the flaws of the justice system but just accepts them instead of trying to fight against corruption. He does not actively work on his lackluster marriage but rather, develops coping mechanisms to keep it afloat. Scobie's relationship with Helen eventually mirrors his marriage to Louise, but like his marriage, he cannot bring himself to end the affair. The situation with Yusef also spirals out of control; Scobie simply watches it happen. He is complacent through most of the events of the novel, except when Ali is killed. Even Scobie's choice to commit suicide seems futile; he does not particularly want to die, but because he cannot conceive of choosing between God and Helen, he chooses to opt out completely.
Responsibility
Scobie’s profound sense of responsibility is a manifestation of his pride. He feels pity for Louise and Helen and takes the responsibility of their happiness squarely on his shoulders, even though he does not love Louise and his love for Helen means eternal damnation. Scobie often feels overwhelmed by this sense of responsibility and wonders why God gave it to him. Greene himself identifies Scobie as "a weak man with good intentions doomed by his big sense of pity."
Surveillance
The colony is full of gossip and spies, and surveillance and observation are key themes of the novel. Everyone knows everyone else’s affairs, and even the priest, Father Rank, is a great gossip. False rumors surround Scobie from the beginning of the novel, but he does not care until those rumors start to contain a kernel of truth. After he has become entangled with Yusuf and Helen, Scobie constantly believes that people are watching him, which leads him make rash decisions that have terrible consequences - like Ali's death. Scobie certainly is being watched – everyone in the colony knows he is having an affair, for example – but Scobie misinterprets the gravity of his failings. He believes that his sins are so vast that his mere existence is an insult to God - which ultimately leads him to take his own life.
Self-awareness
Some of Greene’s characters are self-aware: Louise understands Scobie does not love her and understands how to alleviate her own suffering; Helen completely understands the truth about her relationship with Scobie, even if she doesn't always like it. However, the novel’s protagonist lacks self-awareness. Greene spends a great deal of the novel calling attention to Scobie’s ineffectiveness as a police officer; his limited perspective often causes him to miss the big picture. Louise understands Scobie better than he knows; she comments glibly to Wilson that Scobie only sees what he wants to see. Meanwhile, Scobie's affair with Helen comes as a shock to him, as if he was not complicit in starting it. He wilfully ignores Wilson’s true identity for much of the novel, and he does not fully accept how dangerous Yusuf is until it is too late. In the second half of the novel, Scobie vacillates between leaving Helen and staying with her. With Scobie's decision to commit suicide at the end of the novel, Greene seems to suggest that Scobie did not really know himself at all. Father Rank muses that Scobie loved God more than anyone else, a statement that Scobie no doubt would have been surprised to hear.
Religion
In the novel, Greene divides his exploration of religion into two separate planes. There are the rituals and teachings of the Catholic Church and then, there is the private relationship that exists between God and man. The Church provides rules, structure, and order, but Greene suggests that organized religion cannot account for all the complexities of the human condition. Scobie's relationship with God defines him and leads him to choose suicide in order to avoid a life in which he flouts the principles of the Church. However, Father Rank suggests that God understands that Scobie's suicide was ultimately a result of his overwhelming faith. Greene makes the controversial assertion that the Church's definition of faith is limited and that God may bend some of his "rules" for his children. While Louise is the character that actually follows the Church's rituals, Scobie cannot even bear to keep living with the realization that he has disappointed God.
Isolation
For all of the physical entanglements between the characters in The Heart of the Matter, they are all profoundly isolated from one another on an emotional level. Even when they try to connect, they suffer from a breakdown in communication. In this way, Greene seems to suggest that many of these characters would be better off alone -Scobie is most happy when he in the darkened quiet with just Ali by his side. Helen is happier without Scobie's tortured love for her, Louise finds contentment away from the colony and her husband's pity (and only returns once she hears about his affair). In addition to being isolated from each other, Greene's characters are also isolated from God - especially Scobie. He believes his sins to be so severe that he cannot live knowing that he has disappointed God. Meanwhile, Louise goes through the rituals of her religion but does not seem to find any peace.
Failure
The novel is not a particularly "happy" one; almost all of the characters fail in their endeavors (even when their goals are completely attainable). Louise wants Scobie to get a promotion but right after he gets it he commits suicide and she does not get to be a Commissioner's wife. Even with all his poetry, Wilson cannot make Louise love him. Helen loses Scobie and ends up with Bagster, despite trying to resist the drunken man's inelegant overtures. Scobie fails in almost all of his endeavors, especially those centered around his "responsibility" for others. He fails at being a good husband, a good employee, and a good Catholic. Ironically enough, Father Rank suggests that Scobie may even fail at being damned for his sins! Overall, Greene suggests that failure is a part of life. Human beings can only seek to know themselves and strive to find happiness wherever they can.
