What moral does the Chorus express about the life and downfall of Oedipus in Oedipus Rex?
You might want to consider the final words of Choragos, the leader of the Chorus, in this excellent play. After the blinded, crushed and broken Oedipus exits the stage, wishing himself to be exiled as he pronounced this should be the fate of the murderer of Laius, Choragos is left to deliver the last words of the play which also contain the moral lesson that is drawn from the life and downfall of Oedipus:
Let every man in mankind's frailty
Consider his last day; and let none
Presume on his good fortune until he find
Life, at his death, a memory without pain.
The transformation in the circumstances of Oedipus therefore leads to this moral lesson. The lesson is clear. We should never count our lives as being happy or "presuming on our good fortune," until we die, because, as the play has evidently shown, bad fortune can strike at any moment and bring with it such a reversal of circumstances that can transform our lives utterly.