This strategy is based on the idea that all well-written articles, essays and chapters of books are structured in the following way:
introduction
body
conclusion.
This means that the central ideas should be presented three times:
noted briefly in the introduction
discussed in detail in the body of the text
reviewed briefly in the conclusion.
The beginning and ending paragraphs of a text should provide summaries of its central ideas.
The strategy here is to carefully read:
the first few paragraphs of each chapter or section
the final paragraph or conclusion of each chapter or section.