Why does Sophocles concentrate on life of Oedipus after his becoming King of Thebes? Consider that many of the events in the traditional story of Oedipus(killing of his father, solvin the riddle of...
Why does Sophocles concentrate on life of Oedipus after his becoming King of Thebes?
Consider that many of the events in the traditional story of Oedipus(killing of his father, solvin the riddle of the Sphinx, marryin his mother, etc.) have already occured when the play opens. Why?
bchan182 is right! The structural requirements of a Greek Tragedy compel Sophocles to focus on Oedipus' downfall. And yet, there is a more general reason that the play opens with Oedipus having reached the end of his rope in watching the people of Thebes suffer through the plague. He is sure that someone/ some event is responsible for this curse upon his people and he is determined to find out what he/it is. This is the inciting incident of the play, and all drama should begin with this moment of instigation.
An interesting approach that Sophocles takes in this play is that he, of necessity, withholds some of the exposition (background to the opening scene of the play) -- and you mention these events in your question. The reason that Oedipus Rex does not supply the audience all the exposition (as a play might usually do) in the opening scenes is that these events must be discovered by Oedipus, since he does not know or understand the significance of them, as would commonly be true for a protagonist and his own personal history.
eNotes actually has a nice clear diagram of the required rising action of a dramatic text, and you'll find just below the link to the "dramatic structure" page. I've also provided some links to more information about the play and the opening scenes.
Another reason Sophocles would choose to focus on this particular part of Oedipus's life has to do with his audience. Audience members who were coming to see this play would already be familiar with the story of Oedipus, the king. The stories of his life and misfortune would already be known to them. Thus, they would already have heard the background information that seems new to us, perhaps, and is certainly new to Oedipus himself. Sophocles doesn't need to provide it for his audience to understand what is happening to Oedipus, because they already know.
Therefore, Sophocles's achievement doesn't have to do with the details of the story itself, but rather how he builds tension, leading up to the climax and the audience's catharsis—the moment when the whole truth finally comes out, and the audience feels purged of all the tension (most of which has been the result of dramatic irony: when the audience knows more than the character does). This can only happen once all the details come out, once all the witnesses have a chance to speak and if Sophocles began the play months or even days before, that sense of a quick escalation and heightened stakes would not exist.
Because the story is focusing mainly on his downfall, caused by his tragic flaw, hubris. It is a greek tragedy, and therefore focuses on the downfall of the tragic hero, everything else is just background information.