Religion and Love (Sacred and Profane)
The novel is primarily a love story that chronicles the relationship between Frederic Henry and Catherine Barkley through courtship, consummation, reaffirmation and finally separation by Catherine's death. Throughout the story, the war serves as a catalyst to their relationship not only creating the circumstances that bring them together emotionally but force their temporary separation as well. During the course of the story, Frederic's ideas about love are influenced not only by his growing feelings for Catherine, but also by his conversations with the priest and later with Count Greffi. The priest informs Frederic that the true nature of love, such as the priest has for God, is one in which you desire to serve the object of your affections and the Count qualifies that sentiment by advising Frederic that love for a woman is an act of devotion on par with religious feeling. These sentiments come to a head during the crises of Catherine's protracted labor when Frederic, who previously espoused no particular religious feeling, prays to God for her safety.
Loyalty and War
When we first meet Frederic he is an officer in the Italian army serving in the ambulance corps and the United States has not yet entered the war. Although the novel takes place during the first world war, its action is centered on the northern Italian-Austrian front which though horrific in its own right, was considerably less intense than the fighting in France between the French/British and the Germans. Catherine calls it a "silly front." Frederic admits to Catherine that he doesn't know why he joined the army and thinks that perhaps it was only because he was in the country and spoke the language. His first experience with combat is cut short when a shell wounds him before the attack even begins. Later, when he returns to the front after the Italian army has suffered several military reverses and great loss of life, he gleans the increased pessimism and defeatism running rampant through the troops. Typical of novels set in the First World War, Frederic becomes disillusioned, though unlike other stories from that era such as Erich Maria Remarque's All Quiet on the Western Front or Frederic Manning's The Middle Parts of Fortune, Hemingway's central character is not of the country for which he is fighting. Thus, when Frederic escapes the summary execution at the river and makes a "separate peace", his status as an American citizen aids him in shrugging off any lingering feelings of responsibility.
Death and Mortality
Death is a constant in the story beginning with Passini's violent demise in the dugout and continuing through Aymo's death during the retreat. Both these deaths are from the war and are, in Frederic's estimation, random and unavoidable. Frederic cheats death twice in the story; first, when he survives his wounds and second, when he escapes the executioners. Whatever sense of empowerment this might have yielded, it is undermined when he learns the true nature of mortality when Catherine dies during childbirth. Her death leads Frederic to conclude, as did Hemingway after his own experiences in the war, that each man owes life a death and that sooner or later we all must pay.