War
This piece is primarily an exposé on the horrors of war and the way it can devastate communities. World War II was a battle between governments, but because war is so pervasive, it extended to civilians who had no part in fighting it. At the time of the atomic bombing, Japan and the United States were fighting a total war, which means that typical constrictions on what type of weapons can be used and who could be targeted vanished, and the intention was to force surrender at all costs. This type of warfare can tear apart families and dramatically ruin lives, as is made clear in Hiroshima.
Selflessness
Many of Hersey's six subjects who have not been terribly injured themselves show extraordinary selflessness in wake of the bombing. Mr. Tanimoto spends many days in Asano Park, ferrying the wounded across the river and bringing them food and water. Dr. Sasaki treats thousands upon thousands of injured patients at the Red Cross Hospital, straight through many sleepless nights. Father Kleinsorge and the Jesuit priests take in more than fifty refugees at the Novitiate. All of these selfless acts exemplify tragedy's power to bring out the best in a person.
Resilience
Though their city was completely destroyed and so many of their neighbors died, the citizens of Hiroshima still showed immense strength when they came back together to rebuild their ruined homes and lives. John Hersey notes at the end of Chapter 4 that the one sentiment that all the survivors seemed to share was pride in their community's resilience. Though war can deal much damage, it can also bring people together to show their fortitude and work tirelessly toward the common goal of recovery.
Faith
Religion is a pervasive theme in Hiroshima: Father Kleinsorge is a Jesuit priest, Mr. Tanimoto a reverend, and even Miss Sasaki eventually becomes a nun. It is no coincidence that Hersey chose people of faith as a few of his six subjects. During war, faith can be both a comfort and a curse to people. They latch on to it for some sort of hope, but they also question why, if there is a God, he has allowed something like this to happen. In this case, religion ends up being an essential motivator for the subjects of Hiroshima, driving them to better their own lives and to help others in wake of the disaster.
Sacrifice and Stoicism
Japanese cultural norms play a role in the way citizens of Hiroshima respond to the tragedy. As Mr. Tanimoto notes, because he is Japanese, he feels shame at the fact that he is uninjured while others are, and he works to atone for this by helping his severely wounded neighbors. The Japanese cultural norm is to quietly endure one's own pain, and Hersey frequently references this in his depictions of the severely injured survivors in Asano Park: they stay silent, despite their agony. This sort of stoic, sacrificial mentality also figures into the citizens' response to the Japanese surrender, viewing it as a sacrifice that Japan must make for the greater good of peace in the world.
Uncertainty
Because the atomic bomb is a brand new kind of weapon, there is much uncertainty in the aftermath of its first use in Hiroshima. Citizens first wonder what it was that destroyed their city, and then must live with not knowing how it will affect their bodies, their health, and their lives in the years to come. Hersey's subjects spend a lot of time searching for answers, which takes a toll on their ability to fully recover.
Life Goes On
The addition of Chapter 5, "The Aftermath," supports the idea that, even after tragedy, life goes on. The survivors struggle to cope with what has happened to them, but eventually find ways to provide for themselves and their families, easing their minds as they continue living life. The atomic bomb momentarily slowed survivors' lives, but it did not stop them, and all that occurred in the forty years following the bombing is a testament to this.
