The core concept is understanding the purpose of main ideas. The main idea of a paragraph represents the central point the author aims to convey. Option C correctly identifies this purpose. Option A focuses on details rather than the core message. Option B may or may not be part of a main idea, but it's not always the primary purpose. Option D focuses on a technical analysis rather than understanding the content. The correct answer is C because identifying the main idea enables the reader to grasp the essence of the paragraph. Identifying the main idea is critical to understanding the author's overall message.