Oedipus Rex is arguably the most famous tragedy ever written. At the end of the play, we meet Oedipus's two daughters, Antigone and Ismene. Creon sends for the girls after Oedipus realizes the horror of his incestuous acts and Jocasta has killed herself because he thinks the girls might bring Oedipus some comfort. Their presence here reinforces several themes from the play.
First, they are the embodiment of the theme of ignorance and knowledge. They have lived peacefully as the daughters of the king until the revelation that their father is actually their brother. Throughout the play, Oedipus has consistently wanted more information; now that he has it, he is miserable. The same is true of his daughters. Now that the truth is known, their lives are unalterably changed.
The second theme the girls represent is that every action has consequences. Just as they are for Oedipus, the consequences for Antigone and Ismene are tragic. Oedipus, now that he understands what he has done, outlines the consequences his daughters will suffer from his actions.
Although I cannot see,
I think about your life in days to come,
the bitter life which men will force on you.
What citizens will associate with you?
What feasts will you attend and not come home
in tears, with no share in the rejoicing?
When you’re mature enough for marriage,
who will be there for you, my children,
what husband ready to assume the shame
tainting my children and their children, too?
What perversion is not manifest in us?
Your father killed his father, and then ploughed
his mother’s womb—where he himself was born—
conceiving you where he, too, was conceived.
Those are the insults they will hurl at you.
Who, then, will marry you? No one, my children.
You must wither, barren and unmarried.
Oedipus asks Creon, his brother-in-law/uncle, to take care of the girls, find them husbands, and ensure that they will not have to live as paupers on the streets.
Finally, the appearance of the girls is the picture of innocence contrasted with Oedipus's great guilt. His guilt, of course, prompted him to gouge his eyes out, so the picture of this bloodied, blind man groping to touch his innocent daughters' faces for the last time is the embodiment of guilt and innocence in this play.