What do u think the last lines of the novel mean?

In her detailed descriptions of Charlestown and Lexington, Forbes focuses on the human cost of war for both sides. When the bodies of soldiers are described, Forbes usually does not specify whether they are British or American. Although the battles were caused by political disagreements, their carnage goes beyond politics. Although it is implied that Johnny will lose his physical scars after the operation, he has been psychologically scarred in a way that no doctor can mend.