The Exodus or closing lines of Antigone emphasize the play's overall theme and stress the cause of Creon's tragic downfall.  The Choragos (in some translations also called "Leader" or simply "Chorus") observes:

"Knowledge truly is by far the most important part of happiness, but one must neglect nothing that the gods demand. Great words of the over-proud balanced by great falls taught us knowledge in our old age."

In some translations, the word "knowledge" is "wisdom," which many find more fitting.  Creon obviously possesses much knowledge, but he does not use it in a way fitting to the gods.  He knows what to do when it comes to Antigone's sentence.  Not only has he been advised by his counselors and son to show mercy to his niece, but he also received a clear message from Teiresias regarding his actions.  Unfortunately, Creon's tragic flaw of pride causes him to act unwisely, and he defies the gods.  Thus, according to the Choragos's statement which completes the play, Creon cannot have happiness because he "neglected" to obey the gods (which would have shown wisdom, not simply knowledge).  The final words of the Choragos are the moral of the play--pride brings about one's downfall.  Creon was too proud to admit that his niece was obeying the gods and acting morally when she tried to bury her brother's body. And then, he was too proud to change his sentence when advised to do so because he thought that it would make him appear weak.  The very last words, "in our old age" most likely advises the audience to be willing to listen and change even if a younger person is the one showing an older person the correct way to act.  Sophocles implies that wisdom does not necessarily come with age but that it comes from listening and observing.