The main theme of Paulsen's 'Soldier's Heart' is the transformation of a young man due to the experience of war. War changes the protagonist in many ways. Physically, he endures hardships and possible injuries. Emotionally, he has to deal with the trauma of seeing death and destruction all around him. Socially, he may find it difficult to reintegrate into normal life after the war. All these aspects together show how war can have a profound and long - lasting impact on an individual.
The main theme is often about the psychological and emotional impact of war on a young soldier. It shows how the experiences in the military, such as combat and the harsh military life, can change a person deeply.