What significant realization does Oedipus come to by the end of the play?

Oedipus's realization that he fulfilled the prophecy is central to the unfolding tragedy of the play. Throughout "Oedipus Rex," he is initially portrayed as a confident and determined leader, dedicated to uncovering the truth in order to save Thebes from a plague. However, his relentless pursuit of knowledge ultimately reveals that he has unwittingly killed his father and married his mother, thus fulfilling the oracle’s ominous prediction.

This realization signifies a dramatic turn in Oedipus’s journey from ignorance to knowledge. It emphasizes themes of fate versus free will, as he attempts to escape the prophecy but ends up enacting it regardless of his efforts. The tragic irony lies in how Oedipus's strengths—his problem-solving skills and determination—become the very factors that lead to his downfall. His journey culminates in a deep understanding of human limitations against the decrees of fate, which solidifies the play’s tragic essence.