The main idea is what the story is mostly about, or a quick summary of what happened. In contrast, the theme is the author's larger message that he or she wants the reader to take away.

Read the following passage.

The last time George saw Charity, they were eight years old, building forts of dirt and sticks in the corner lot. When Charity's family moved to Texas, George was heartbroken. There were 500 miles between them, but to George, she may as well have moved to the moon. For a time, George mourned the loss of their friendship. But much to his surprise, a letter appeared in his mailbox the next week. It was the first of many sharp, funny letters in which Charity's unique personality leaped off the page. Through this correspondence, George followed six years of events in Charity's life: her family's many moves, her struggles in school, her triumphs playing the violin. He hoped that she looked forward to his responses as much as he looked forward to hers.
What is the main idea of the passage?
A
People can remain good friends even if they are separated.
B
A boy remains friends with a girl who's far away by writing letters.
C
As people grow up and go through hard times, they lose their innocence.
D
A boy's relationship with a good friend ends after she moves away.

the passage revolves around the enduring friendship between George and Charity despite their physical separation. It highlights how George maintains their friendship through letter writing, demonstrating the resilience and depth of their bond. The passage focuses on the theme of friendship transcending distance, as George continues to connect with Charity despite the 500-mile gap between them. Therefore, option B, "A boy remains friends with a girl who's far away by writing letters," best summarizes the central focus of the passage.