What does the quote "As for this marriage with your mother—have no fear. Many a man before you, in his dreams, has shared his mother's bed. Take such things for shadows, nothing at all— Live, Oedipus, as if there's no tomorrow!" (From Oedipus the King, by Sophocles) mean

Jocasta treats incest with lightness

Explanation:

Fear? What should a man fear? It’s all chance, chance rules our lives. Not a man on earth can see a day ahead, groping through the dark. Better to live at random, best we can. And as for this marriage with your mother—have no fear. Many a man before you, in his dreams, has shared his mother’s bed. Take such things for shadows, nothing at all— Live, Oedipus, as if there’s no tomorrow! (Oedipus the King, 1068–1078)

The audience, familiar with the Oedipus story, almost does not want to listen to these self-assured lines, spoken by Jocasta, wherein she treats incest with a startling lightness that will come back to haunt her. What makes these lines tragic is that Jocasta has no reason to know that what she says is foolish, ironic, or, simply, wrong. The audience’s sense of the work of “fate” in this play has almost entirely to do with the fact that the Oedipus story was an ancient myth even in fifth-century b.c. Athens. The audience’s position is thus most like that of Tiresias—full of the knowledge that continues to bring it, and others, pain.

At the same time, it is important to note that at least part of the irony of the passage does depend on the play, and the audience, faulting Jocasta for her blindness. Her claim that “chance rules our lives” and that Oedipus should live “as if there’s no tomorrow” seems to fly in the face of the beliefs of more or less everyone in the play, including Jocasta herself. Oedipus would not have sent Creon to the oracle if he believed events were determined randomly. Nor would he have fled Corinth after hearing the prophecy of the oracle that he would kill his father and sleep with his mother; nor would Jocasta have bound her baby’s ankles and abandoned him in the mountains. Again and again this play, and the other Theban plays, returns to the fact that prophecies do come true and that the words of the gods must be obeyed. What we see in Jocasta is a willingness to believe oracles only as it suits her: the oracle prophesied that her son would kill Laius and so she abandoned her son in the mountains; when Laius was not, as she thinks, killed by his son, she claims to find the words of the oracle worthless. Now she sees Oedipus heading for some potentially horrible revelation and seeks to curb his fear by claiming that everything a person does is random.