Why does Chinua Achebe tell us the story of how Chike's parents were married in the middle of Chike's School Days?

In the middle of the story, Chinua Achebe relates the circumstances surrounding the marriage of Chike's parents in order to provide us some sort of context for Chike's seemingly strange habits.

Accordingly, Chike and his family live in a traditional Nigerian village where children are regarded 'as the common responsibility of all.' One day, thinking to do him a kindness, a neighbor lady offers Chike, then four years old, a piece of yam.