Usually the purpose is to persuade the admissions committee that you are an applicant they should choose. You may want to show that you have the ability and motivation to succeed in your field, or you may want to show the committee that, on the basis of your experience, you are the kind of candidate who will do well in the field. Whatever the purpose, it must be explicit to give coherence to the whole statement.Pay attention to the purpose throughout the statement so that extraneous material is left out. Pay attention to the audience (committee) throughout the statement. Remember, your audience is made up of faculty members who are experts in their field. They want to know that you can think as much as what you think.