Chapter twelve is the central chapter of the novel. It relates events which were only hinted at in the first chapter when Lena Grove arrived in town and saw the column of smoke. Remember that earlier we learned that Joe Christmas had killed Joanna Burden. The next several chapters had provided the impetus and settings to the crime.
As chapter twelve begins it deals with the absolute dishonesty of Joanna Burden. Her and Joe’s relationship went through three distinctive phases. The first was the seduction which we heard about in the last chapter. The second came during the wild “throws of nymphomania.” The last phase was Joanna’s effort to change Joe.
During phase two, Joanna, in the thrill of her sexual relationship with Joe would often cry “Negro! Negro!” That pointed out that she on the whole enjoys being dishonored by someone with Negro blood. Despite her heritage, which should have trained her to accept the Negro as equal, this howl suggests that again Joe is not being acknowledged as a person of equality. This in itself changes his relationship with Joanna.
The crucial change comes during the third phase. The reader should remember that Joe always thought of women as being destructive to his sense of order. The dietitian, Bobbie Allen, and unknown prostitutes have forced him to be suspicious of the influence of women who seem to infringe his sense of an ordered life. For about two years, Joanna and Joe’s relationship obey the rules of an ordered (though nontraditional) pattern, but when Joanna broke this pattern with her demands that Joe Christmas take over her finances, go to a Negro school, and finally that he pray with her in order to be saved, he again reacted violently to this infringement of his concept of an ordered existence. Prayer is particularly offensive to Joe. This was because of his earlier childhood experience with Mr. McEachern when the elder man beat him unmercifully because of his refusal to recite the catechism.
Joe also views women as being capable of tearing down his own individuality. He thinks in this chapter that it would be easy to give in to Joanna and live a life of security and ease. But then he thinks that if he did give in, he would be denying everything that he has stood for during his life. As a result, when Joanna tries to compel him to change, he must kill her or else his own sense of security and isolation is violated. On the simple plot level, Joe kills Joanna in self-defense because she did attempt to kill him. She would have succeeded if the gun had not failed to fire. In the purest legal sense, Joe kills Joanna out of self-defense.
While he could have run, remember he has spent his life running. He now feels that he must take his stand. He must assert his own values. He does this even if it means killing the person who is trying to go against his order and serene way of life.