Table of contents is the answer
One theme from Things Fall Apart is the complexity of Igbo society before the arrival of the Europeans. To assist this theme, Achebe incorporated the detailed explanations of the trial process and justice codes, family rituals, marriage customs, preparation processes of food and its production, divided leadership for the community, belief in religion and its practices, and the chances give to every man to be able to climb the clan’s ladder of triumph by his own doing.
I think that number 3 is the answer you're looking for.
The theme is a more specific topic....theme is the main messaged passed on through writing while a topic is the major subject explained in writing.
