Psychology is the study of the human mind – not the brain. Psychologists study cognition (thought), emotion, feeling, and the motivations that make us do what we do. It is a field that can be helpful in many ways, even if you don’t intend to be a clinical psychologist. Understanding human motivation and emotion can be deeply important in sales, politics, law, and many other fields. Of course, it can also be helpful if you want to work as a therapist, or as an organizational psychologist who uses psychology to improve organizational performance and efficiency.
This video by Professor Caroline Catmur of the University of Surrey is a good overview of why you might want to study psychology.
This article from Very Well is a good summary of some of the reasons to study psychology.