It gives this section of the interview a scholarly tone.
According to the excerpt from "Interview with Simon Ortiz," Ortiz makes use of formal language in order to demonstrate that he has the knowledge and has accomplished academic study to talk about people in Africa and the Americas. Therefore, through his academic language he proves to be an accredited source, which validates his explanation.
Formal style is a way of writing which involves professional and 'formal' words, meaning it's not casual like one would typically speak. Objective tone has to do with neutrality. When one uses objective tone they are simply presenting the facts rather than opinion. These two techniques make for reliable and convincing writing.