Hello. You have not submitted the excerpt to which this question refers, which makes it impossible for it to be answered accurately. However, I will try to help you in the best possible way.
The central idea of a text refers to the main subject, the theme that the text is addressing. This theme is developed by a character through arguments, where that character discusses the entire composition of the theme, in addition to applying it at some point in his life, or of life and another character.