This chapter shows Razumihkin's intense feelings for Dunya and helps prepare the way for him to take over caring for the family while Raskolnikov is involved with his guilt. The long description of Raskolnikov emphasizes his split personality and describes his dual personality "as though he were alternating between two characters." In using such terms as "split personality," one is using a term that has not yet been coined by Sigmund Freud, but Dostoevsky was fully aware of the quirks of one's personality even though they had no label.
The mention of Raskolnikov's desire to marry the ugly, queer, invalid daughter of his landlady illustrates Raskolnikov's predilection for the weak and the downtrodden and helps to explain his later attraction to Sonya.
Luzhin's attempt to cause dissension between Raskolnikov and his mother by suggesting that Raskolnikov gave money to Sonya, a prostitute, rather than to Katerina Ivanovna, shows what a despicable character he is and how right Raskolnikov was to see this petty, ugly side of Dunya's fiancé. His request that Raskolnikov not be present at their interview is another attempt to alienate Raskolnikov from his family, thus making them more dependent on Luzhin.
The reader should further note that after being constantly with Raskolnikov, it is unusual that we have an entire chapter without his presence. It is necessary, however, so that the relationship between Razumihkin and Dunya can progress, and also prepares us for Raskolnikov's dependence on Sonya.
