As Sophocles' Oedipus the King reaches its conclusion, the old men of Thebes who comprise the play's chorus offer some final observations. The last three lines of the play are a common sentiment in ancient Greek thought and basically state that until a person has passed away, we cannot assess whether a person lived a fortunate or unfortunate life. This, I would say, is the lesson these lines impart to the audience.
As for Oedipus himself, although things look very bleak for him now, those who knew the full story of Oedipus would recall that his life ends on a more positive note. In Sophocles' Oedipus at Colonus, which was staged about 25 years after Oedipus the King, we learn that Oedipus simply vanishes from the earth. We also learn that his death was a peaceful one: "The man passed away without lamentation or sickness or suffering, and beyond all mortal men he was wondrous" (F. Storr translation).
So, while the final three lines provide general advice for all mortals, they may offer some hope with respect to Oedipus, whose life seems to have ended in a happier way than one would expect from the conclusion of Sophocles' Oedipus the King.