Your medical school personal statement needs to sell. Every single word has to sell your reader and answer the question: "Is it worth my time to read one more word of this essay?" To be persuasive is to sell your reader on your next sentence, your next paragraph, your next idea of your medical school essay.
There are schools that require an applicant to submit a Statement of Purpose instead of a PS, the thrust of which is to present an applicant's goals in terms of what major to pursue, what research direction to take, and other specific study and career plans, if any. Therefore, in this case, you are required to submit a similar essay but with greater emphasis on your specific study and career plans. Most applicants are confused with the difference between a PS and a Statement of Purpose. This is not to say, however, that a PS cannot be a Statement of Purpose and vice versa, because as you will discover in the next section, these two can actually overlap depending on the outline you have created.