The concept that humans are the authors of their own choices in a sense that makes them genuinely responsible for what they do — a concept whose acceptance or rejection determines how societies treat sin, punishment, merit, and the justice of holding people accountable for their actions.
Free will is not a philosophy seminar topic. It is the concept that decides whether we punish criminals or treat them, whether we praise success or attribute it to luck, whether sin is real or a category mistake, and whether anyone deserves anything. What societies believe about free will shapes their institutions. And what neuroscience is discovering about the brain is forcing those beliefs to change.