Up until now Achebe has created many chapters in opposition or juxtaposition to one another in order to illustrate the kind of life that Obi lives and has lived through the literary device of parallels and opposites. At this point in the novel, however, everything seems to take on a linear structure as the novel travels through the ends of Obi's recent past.
In chapter 13 there is quite a bit of foreboding. First, Clara begins to cry again because she believes she will ruin Obi's life and cause him family strife, which indeed she does, through no real fault of her own. Then, Obi's mother is quite ill and, at the end of the chapter, there are women who come to sing for her. However, the women that come to sing for her are the singers who have just come from a funeral. Achebe has them stop by the house as if to foreshadow Obi's mother's own death. Also, the song that they sing is relevant to Obi's own dénouement. The lyrics to the song go as follows: "For a kinsman cannot be bought in the market, / Neither is a brother bought with money." This verse exists to remind the reader of Obi's eventual "selling" of himself proving this verse wrong.
Also, it is important that this is the first time in the novel that Obi cannot find enough strength within him to stand up with conviction for what he believes. He has lost his will in many ways and does not want to have his mother's blood on his head. The story about the razor blade that caught his mother's hand begins to take on a different meaning here. The blood is no longer a bond but a threat.
Finally, there are the conversations that Obi has with his father. It is important to realize that Obi uses the language of Christianity and the language of "enlightenment" (the same language he had used to criticize the colonialists) in order to convince his father that his marriage to Clara is not something that is wrong. He, like Achebe, knows how to use the tools, the language, and the culture of the outsider, of the colonizer, to his advantage.
At the end, Obi's father understands and provides a parallel of his own: he tells the story of when he leaves his house with a curse upon his head for wanting to be a Christian. This is very much like the way Obi is being treated for wanting to marry an osu. It is almost as if Obi's father has given in and almost as if he understands. However, he claims that it is because of all of this trouble that he truly knows and understands what Christianity means. Perhaps then, Obi's father is not only telling him that he, in some way, understands, but also that he must truly understand what he is doing. Yet, Obi seems to have the conviction to fight his father, but his conviction to fight his mother is weak and dying.