Worth noting in the Proem to the Summa:
1. St. Thomas intends to write a book for beginners in theology. I.e., those just beginning to study theology. He supposes that his readers are the sort of people who read other academic treatises on theology (e.g. Peter Lombard's Sentences and other similar works).
2. St. Thomas finds that many theology students are hindered in their studies by the poor organization of these books, by their focus on useless questions, by their repetitiveness.
3. St. Thomas intends to teach by the inner order of his subject matter. This means that the organization of questions and topics is according to general principles and essential features, not according to chance associations or interests (not "as the plan of the book might require" or "as the occasion of the argument might offer"). This means that the text of the Summa has an inward intelligibility that is clearest to the person who has already understood its content. Its ordering is Sapiential, i.e. flowing from the order of the subject, rather than Occasional, i.e. flowing from the needs of the moment or the convenience of the reader.
4. Still, because the book is for beginners, Thomas does not presuppose basic theological principles, but works through everything from first to last. He does, however, presupposed a reasonably thorough knowledge of Aristotelian philosophy.