Sir Richard C. Jebb, Commentary on Sophocles: Oedipus at Colonus

Here it becomes important to notice an innovation made by Sophocles. In the epic version of the story, as also in the versions adopted by Aeschylus and Euripides, Oedipus cursed his sons at Thebes, before the strife had broken out between them.¹ He doomed them to divide their heritage with the sword. Their subsequent quarrel was the direct consequence of their father's curse. But, according to Sophocles, the curse had nothing to do with the quarrel. The strife which broke out between the sons was inspired by the evil genius of their race, and by their own sinful thoughts². At that time Oedipus had uttered no imprecation. His curse was pronounced, after the breach between them, because they had preferred their selfish ambitions to the opportunity of recalling their father (421)³. Long before, when he was driven from Thebes (441), he had felt their apathy to be heartless; but he had uttered no curse then. There is a twofold dramatic advantage in the modification thus introduced by Sophocles. First, the two sons no longer appear as helpless victims of fate; they have incurred moral blame, and are just objects of the paternal anger. Secondly, when Polyneices—on the eve of combat with his brother—appeals to Oedipus, the outraged father still holds the weapon with which to smite him. The curse descends at the supreme crisis, and with more terrible effect because it has been delayed.