Identifying Author's Purpose in Nostalgia

Read the following excerpt from a fictional short story:

"The sun was setting behind the old oak tree, casting long shadows across the grass. As Sarah sat on the porch, she thought about the summer she had spent at her grandmother's house, filled with laughter and adventure. The sounds of the neighborhood echoed around her, reminding her of the sweet moments that made childhood so magical."

Based on this excerpt, what is the author's primary purpose in this passage?