In the body paragraph you will basically express your interest in taking admission. Important things you are going to mention include the basis for applying to the school. Why do you think this school can build up your career? List down all academic achievements and special skills that would help in making your letter stand out from rest of the applicants.
The Letter of Intent is not binding, and rather silly at the worst of times. An LOI by definition only registers intent to purchase, and it specifies this intent weakly, and due to its ambiguity should be avoided.