Like most plays, Oedipus Rex is narrated in the Third-Person Objective point of view. In Third-Person Objective, we do not directly hear any characters' thoughts and feelings. Instead, thoughts, feelings, and motivations are revealed through actions and dialogue. Since this is a play, we are only provided actions and dialogue to tell us about things such as characterization and themes. However, the dialogue does primarily focus on Oedipus. The focus on Oedipus allows us to see his transformation as a character and his revelation, which impacts the play by helping us see the depths of the tragedy.
We know that Oedipus is the focus on the narration because the play opens with him asking his citizens and the priest what is ailing them. Oedipus is also the main source of the conflicts, first with Tiresias and then with Creon. Oedipus begins an argument with Tiresias after Tiresias delivers his prophecy declaring that soon Oedipus will realize that his own actions are the source of the gods' anger and the plague. Oedipus accuses Tiresias of being bought to deliver false prophecy by Creon whom he accuses of plotting his overthrow. Next Oedipus gets into a verbal conflict with Creon as he confronts Creon for his assumption that he is trying to take the thrown. Finally, Oedipus begins to realize the truth about Tiresias's prophecy and who he actually is. His realizations culminate in several speeches, especially one long speech describing his misery at the realizations of his transgressions against his parents and the gods, as we see in his lines:
... For I don't know with what eyes I could look and see my father when I go down to Hell, nor again my poor mother; to those two my deeds are beyond what hanging could punish. (1393-96)
Hence, since the Third Person Objective point of view focuses on Oedipus, it gives us the opportunity to learn what his character is like and to witness his self-realization, which makes the tragedy even more poignant.