This is in general, but in specific you need to explain your goal in life, and sorry your goal is not to study, your goal is what is going to be done with that study, what you are trying to accomplish in life, what you feel you will be, where those studies are going to take you. Are you going to be passionate about the courses or passionate about what you will do with those courses?
Also you must show that you had done something to this world, and that you are going to do more, you are going to help someone get out of his or her vicious circle, or you will improve on a medical field. You must show that your ambition is to be the next Einstein, or Thomas Addison, or Bill Gates, or Steve Jobs. You must show your admiration on something in life, or your dissatisfaction with the status quo and your hope in creating a better life for humanity.