What is the role of the chorus in Antigone?
The first thing to note is that Greek tragedy evolved out of choral performance. Having actors who played individual roles was an innovation that began within Sophocles' own lifetime. You could even argue that the chorus is the center of the drama.
The chorus first serves as a form of spectacle, as in ancient productions choral odes were sung with the chorus dancing as they sang. This song and dance was deeply rooted in tradition and religious ritual and thus emphasizes the sacred roots of tragedy. As Sophocles' plays were originally performed at a festival in honor of Dionysus, in a religious rather than secular context, the chorus functions to celebrate the gods and often expresses a particularly pious viewpoint, thinking about how the gods might be connected with or concerned about various events in the play. On a dramatic level, they often function as a narrative voice, explaining what happened before the start of the play and discussing events that occur offstage.
Finally, the chorus expresses the viewpoint of "everyman", of the society as a whole as an organic construct with certain beliefs and moral values. While both Creon and Antigone are outliers in their viewpoints, with Creon more rational and pragmatic than average and more an advocate of human rational law than tradition and Antigone more personally religious and devoted to family than average and more willing to rebel against human convention, the chorus expresses what would have been the "common sense" viewpoint of the period, against which we can judge more extreme positions.
In ancient Greek drama, the chorus is a group that comments collectively on the play's action and context. The role of the chorus is to provide information not revealed in dialogue, such as context within mythology, narration, and the characters' thoughts.
In Antigone, the chorus consists of Theban elders. They provide background information connecting Antigone's story to other myths and comment on the play's action. The chorus in Antigone even participates in the action of the play occasionally; for example, at one point Creon consults them and they provide their support for his decision, although they later oppose Creon when he considers punishing Ismene. The play closes with a monologue by the Theban elders about how the gods' punishment can bring wisdom.