The purpose of the prologue in Sophocles' play, "Oedipus Rex," is to inform the audience of the events leading up to the main action of the play. The prologue also offers a narrative to these events.
The prologue explains how and why the people of Thebes believe in Oedipus. According to an article on the Virginia Community College System's website, during the prologue the audience learns that Oedipus becomes king because he solved the riddle of the Sphinx, which no one before him was able to do. He is like a god in this way, and the people of Thebes believe he has extraordinary abilities given to him by the gods. For this reason, the people come to him for help. In an article on Temple University's website, it is suggested that Thebes is hoping that Oedipus' greatness will help rid them of the plague. In fact, they are placing all of their hope in him. From the very young to the aged, residents of Thebes are begging Oedipus to use his special abilities once again. The audience learns that even the priest has incredible faith in Oedipus when he tells them a wise king "can act in a time of troubles, and act well." The prologue gives the audience a clear view of what Thebes expects of the king, which is nothing short of a miracle.