In the beginning, before Oedipus had any idea that he was in fact married to his mother and had also put a great curse upon himself, he had a strong sense of pride.
"Ah me! ah woe is me! Ah whither am I borne!"
Oedipus constantly is doing the wrong thing, but he doesn't know that he is. He killed his own father, and then married his mother. Some say that Oedipus is even running from his own fate, which makes things worse.
"How terrible-- to see the truth when the truth is only pain to him who sees
When Oedipus realizes that he was the one responsible for the unfortunate fate of the people of Thebes, he was shocked, and completely blamed himself. His reaction highlighted how blind Oedipus was to the whole situation and the shame he had for himself after finding out.
"This land of ours calls you our savior since you saved it once."
As Oedipus realizes that his wife and mother, Jocasta, knew the truth about their family all along, Oedipus shows his true sorrowfulness and evokes pity from the audience, as he wonders why he was even born, if his whole life is sadness.
Towards the end of the play, Oedipus puts the pieces together and realizes that he is truly married to his mother, and he is the one who killed Laius. He finds out who he truly is, and that for years he was living a lie. He had no idea he was married to the woman that gave birth to him or that he killed his own father and brought the Plague to Thebes.
Oedipus was summoned by the Priest in the beginning of the play. The Priest knows that Oedipus is capable of saving the town, and he trusts him. Oedipus is credible and worthy of the job.