Incomplete applications are not usually considered, and when they are, the fact that they are incomplete reflects poorly on the candidate. Your grades reflect your standing among your peers. Obviously, grades are important, but it is wrong to assume that good grades are enough. There are too many students with good grades out there interested in graduate training. You will nee other qualifications to distinguish yourself.
Most applications ask for a statement of interest.
The request for an personal statement is often misunderstood by student applicants. Students who take the request literally harm their application by appearing unsophisticated and naive. A statement of your interests in your chosen field and how you came about to have those interests. What your goals and ambitions in the field are. How the program to which you are applying can help you to achieve those goals.