Celie's stepmother gets sick and must stay in bed. Celie tells her father to sleep with her, not Nettie, while their stepmother is ill. Celie dresses up for the occasion to entice her father; her father beats her for dressing "trampy," but still sleeps with her. Celie believes that Nettie has figured out that their father sexually abuses her, but everyone is too scared to say anything.
One of the novel's saddest scenes. Recognizing that she is not traditionally attractive, Celie does her best to present herself in a fashion that her father will enjoy in order to protect her sister, and gets beaten for it. Nettie never forgets that Celie has "laid herself down" for Nettie on this and other occasions.
Mr. ____ comes again to ask for Nettie's hand in marriage. Celie's father says no, again, but tells him he can marry Celie, the older daughter, despite the fact that she's had two children. Celie's father pretends he does not know who the father of those children is.
Pa's reasons for marrying Celie off aren't entirely clear, but it appears that, now she is older, Pa is less interested in her sexually—and he wants Nettie to remain at home, so he can begin to sexually abuse her instead.
Mr. ____ says that Celie is unattractive, but her father says she is a good worker, that she can no longer bear children, and that she will be a good wife to Mr. ____, though she isn't very smart and she's a "liar."
Pa does not try very hard to "sell" the idea of marriage to Celie—but he recognizes that Mr. ____ needs helps raising his children, and will do whatever it takes to provide for them a mother-figure.