A huge theme within Harry Potter and the Sorcerer's Stone is that of the power of choice and its impact on our wellbeing, on our lives, and on the lives of others. We are repeatedly given examples of difficult choices and their consequences or positive outcomes.
For example, the book begins with an examination of how choice impacts Harry's early life with the Dursleys. As a ten-year-old orphan living with his terrible Uncle Vernon, Aunt Petunia, and Cousin Dudley, Harry has very little agency; he is forced to live in a tiny cupboard beneath their stairs and is largely neglected. Even after the flood of letters addressed to Harry begin to arrive, Harry is not allowed to open them, and is, in fact, swept off to a small island to sequester him from the truth of his heritage and being: Harry is a wizard. Once imbued with this truth and provided with agency—the ability to choose—Harry's life is radically and irrevocably changed.
More and more instances of the consequences of choice arrive as the book unfurls: We learn that Harry's mother chose to sacrifice herself out of immense love when Voldemort hunted the Potters down, an act that resulted in her own death... but also in Harry being able to survive Voldemort's attack while being rendered mysteriously protected from his touch. We discover that Professor Quirrell chose to serve as a vessel for what is left of Voldemort's decrepit being, an act that results in Quirrell's slow unraveling and eventual death. We discover that Nicolas Flamel, the creator of the sorcerer's stone, makes the difficult decision to destroy it... an act that will eradicate the powers of immortality that the stone imbues and result in Flamel's death, but will otherwise serve the greater good of wizarding-kind.
We see less outwardly dramatic choices as well: When offered friendship by arrogant Draco Malfoy, Harry chooses to reject this relationship—despite its offer of instant power and social climbing in his new school environment—in favor of friendships with the far less popular Ron Weasley and Hermione Granger. Ron and Hermione end up becoming some of the most critical people in Harry's life and a source of continued support for him.
Harry chooses to break the rules during a broom-flying lesson in order to act honorably and rescue the Remembrall of his awkward peer, Neville Longbottom. While this is a risky choice, Harry winds up as the Seeker of the Quidditch team because of the boldness and skill he displays on the broom.
Ultimately, choice becomes an incessant presence within this book, as well as within the rest of the Harry Potter series. Perhaps what J.K. Rowling is getting at here is an important life lesson for us readers as well: We can either let life happen to us, or stand up and choose courageously... even if the choice is one that might result in pain or difficulties for ourselves. There is always power in seizing one's agency, in learning to deal with unfortunate circumstances, and in fighting on the behalf of the forces of good.