So, if a letter or document that nominally or presumably conveys the signer's "intent" or intention to buy, is essentially meaningless and worthless in legal terms, and is not binding on the signer or anyone, and CANNOT be enforced on him, then why would a respectable crude buyer, in the first place, want to waste its precious time and resources (or that of its expensive lawyers) to engage in such a fruitless exercise for the benefit of a seller? Especially for an unknown or obscure seller?
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.