Re-read all the material you have written so far. Then write an introduction answering the question: What is Blatty’s message? All of the body paragraphs will articulate HOW he delivers this message.
I am deliberately giving little guidance because we need a “before” version of your intro that is raw; I will lecture and model introductions next week, and we will edit this one.
Use all the introduction skills and knowledge you’ve learned so far in life. It should be about 2/3 of a double spaced page in length.