The chorus in a Greek tragedy serves many roles. According to Aristotle, one of the chorus's main functions should be to act as a character, even though the chorus was positioned outside of the main action in the orchestra where it sang and danced. As a character, the chorus has many functions. It interacts with other characters; it underscores important moral points; it even sometimes misunderstands things that happen in the action that the audience actually does understand; and it even makes its own wrong assumptions and delivers its own wrong opinions; although, sometimes the chorus holds the correct opinion (Weiner, "The Function of the Tragic Creek Chorus"). Sophocles' chorus in Antigone certainly functions as a character, but also plays the very vital role of interacting with Creon in a way that serves to help develop his character and reach his moment of revelation.
In Sophocles' Antigone, the chorus functions as respected Theban, elderly courtiers. They are especially respected Theban citizens that Creon has specifically summoned to tell them of his ascension to the throne and his law forbidding Polynices' burial, hoping to gain their support. As supporters of their new king Creon, they remain by his side and support his decisions all throughout the play, except for offering a few opinions here and there. For example, the chorus supports Creon when he tells Haemon to stand by his "father's ideas in all things" (649). They also support Creon when in the same speech he condemns violators of the law and warns Haemon not to "yield to women" (688). The chorus refers to Creon's arguments as wise, but then when Haemon declares that all the city feels that Antigone's death is unjust and that she should be honored for doing such a noble deed, the chorus says that Haemon has argued well also and warns Creon of the need to listen to sound counsel, as we see in their line, "If someone speaks in season, you should," which is a line that happens to underscore one of the play's central morals concerning stubbornness (736-737).
Finally, towards the end of the play after Tiresias has announced his prophecy of doom, the chorus advises Creon to listen to good advice and tells him to release Antigone. Because the chorus helps Creon to realize his foolishness and get past his inability to listen to others' counsel the chorus serves to help Creon develop as a character and reach his moment of revelation. The chorus is the prime candidate to serve this function due to the members' roles as respected, elderly noble citizens. Since they are respected, it is more believable that they have the power to eventually influence Creon. Therefore, the chorus is extremely essential in Antigone due to the members' influence on Creon and their portrayal of the story's morals.