Why does Mahfouz employ stream of consciousness narration in the novel and to what effect?

In chapter 1, Naguib first introduces us to the protagonist Said, who is in jail during the very early stages of the novel. In the first chapter specifically, Mahfouz manages to constantly switch and redirect his style of writing, whether it being from first person to second person, or by implementing stream of consciousness narration, including a soliloquy, interior and exterior monologues. The employment of such writing styles in the text, allowed Naguib to achieve a number of significant intended character traits that are to be developed and built upon in the upcoming events of the novel. 

As we are first introduced to Said, we are given insight regarding his expressed hatred towards both Nabawiyyah and Ilish, his wife and former friend respectively. The hatred has been expressed when he says "I swear I hate you all", he also describes his ex wife by saying "that woman who sprang from filth, from vermin, from treachery and infidelity.”(p.152) and “one of the secrets of hell!". After reading these previous lines, readers as audience view Said's character to be filled with hatred. However, Naguib provides contrast to the hating nature of Said's character, where his feelings for his daughter are shown to be filled with love, seen in the line "As the thought of her crossed his mind. The heat and the dust, the hatred and the pain all disappeared, leaving only love to glow across a soul as clear as a rain-washed sky", portraying Said's nature further. This shows how Naguib managed to provide us as audience, with deep insight regarding Said's character, only by providing us with slight detail regarding his feelings and thoughts, achieved by implementing quotes and direct monologues. 

Furthermore, we were firstly introduced to Illish's character through Said's inner thoughts and feelings, which gave a rather negative impression regarding his 'yet to be introduced' character. However, as the audience are given the chance to view Illish's character further in the first chapter, they are provided with Indirect characterization, also mainly achieved by the style of writing that Naguib uses. Later in the first chapter, the first time the audience are encountered with Ilish is when he invites Said to his house, then as the scene progresses, we as audience, manage to see somewhat valid reasoning behind his argument with Said, that we do not have a lot of insight about, other than the fact that Said's inner thoughts and feelings are neglecting it based on Said's point of view solely.