The central idea of the story “Marriage Is a Private Affair” reveals that choice-based marriages can prove successful, even in societies where arranged marriages are the norm, when there is love and commitment between the parties involved. Indeed love can conquer anything.

The story is based on an Ibo society, whose marriage customs require that couples are matchmade. Nnaemeka thus faces stiff opposition from his family, and village at large, about his plans to marry Nene, a woman he has met in the city of Lagos. His father Okeke is so furious that he decides to erase the memory of his son from his mind, especially after Nnaemeka marries Nene in spite of his and the clan’s objections. Okeke even bans his son from his home. Over the years, however, an undeterred Nene works hard to gain the approval of the clan. She makes friends with her husband’s village mates, who are living in the city. She even writes a letter to her father in law, begging him to reconsider their situation, as their children would really want to visit the village to see their grandfather. This letter really touches the old man’s heart. The story ends, with Okeke in a remorseful mood, thinking about his innocent grandchildren and how he just might die “without making it up to them”.

What is the theme of "Marriage Is a Private Affair"?

The main conflict in Chinua Achebe's short story "Marriage is a Private Affair" is between a father and a son. In a broader scope, it also involves a conflict between generations and cultures. The father, Okeke, lives in a small rural village and his life is dictated by the ancient precepts of his culture, including strict rules about marriage. On the other hand, his son Nnaemeka has moved to the modern city of Lagos and looks at the world in a completely different way. He feels as though he is not bound by cultural taboos. He decides to go against the old ways by marrying a girl who is not from his Ibo tribe. This marriage is initially unacceptable to his father but as time passes, and Okeke learns after eight years that he has two grandsons, his heart softens. In the end, Achebe suggests that Okeke will give in and see his son's family. The theme of the story, then, is that love, especially familial love, can overcome cultural and generational conflicts. Acceptance is also a powerful theme of the story as Okeke begins to understand that he lives in a new reality and that old traditions, prejudices and ways of thinking need to be set aside in a rapidly changing modern world.   

What is the central idea of "Marriage Is a Private Affair"?

I tend to to think that one of the central ideas of the story is that it is important to ensure that grudges are not carried between children and their parents.  Okeke seems to understand this at the end of the story, a closing with an eerily sad note that indicates his revelation came a bit too late for his own liking.  Okeke is the aggressor in terms of the conflict between he and his son.  He is the one who made a defiant stand and refused any notion of seeking to bring back together the relationship.  It is in the end of the story, with the realization that he is a grandfather, does he recognize the silliness in seeking to deny the relationship he has with his son.  Perhaps, it is here where Achebe is making the claim that in situations like these, the older generations must recognize the idea that "marriage is a private affair" and accept the fact that children see marriage in such a light.  The ending of the story is one in which time seems to be creeping up on Okeke, to a point where he is fundamentally of losing a relationship that he himself discarded:

The old man at once felt the resolution he had built up over so many years falling in. He was telling himself that he must not give in. He tried to steel his heart against all emotional appeals. It was a reenactment of that other struggle. He leaned against a window and looked out...  Okeke was trying hard not to think of his two grandsons. But he knew he was now fighting a losing battle... His mind immediately returned to the children. How could he shut his door against them? By a curious mental process he imagined them standing, sad and forsaken, under the harsh angry weather—shut out from his house. 

That night he hardly slept, from remorse—and a vague fear that he might die without making it up to them.

In this ending, one sees that Okeke recognizes fully the errors he made in his relationship with his son and grandchildren.  It is in this where the lesson about the choices children make and the need for adults to do what they can to be supportive of these decisions becomes critical.