When the elders question Oedipus about his past, he at first refuses to answer, but finally consents. He admits his wrongdoing, but insists that he killed his father in self-defense and married his mother in ignorance.
The elders here seem strident, even prurient, in their questioning. Their unkindness to the aged, blind beggar deepens the audience's sympathy for Oedipus as he explains his crimes — and his sufferings — from his own point of view.
In essence, this dialogue represents another kind of purification ritual — a painful confession — paralleling the ritual Ismene carries out offstage.