In Sophocles's play Antigone, scenes between the principal actors are separated by brief interludes from the chorus. On a practical level, the chorus dialogue allowed time for the three main actors to change costumes behind the scenes. However, Sophocles also designed the chorus to serve as a living encyclopedia for the viewer; it frequently references mythological works or other plays that Sophocles wants to draw parallels to throughout Antigone.
The chorus is not, however, completely detached from the action of the story itself. In Antigone, Sophocles has designated the chorus to be composed of elderly Theban men. This places them firmly within the context of the central events; they always follow the rule and desires of the ruler Creon. As the play progresses, however, the chorus begins to express divergent thought, most notably as it relates to Creon's decision to sentence Antigone to death for giving Polynices a proper burial. The chorus gives voice to the viewer's own discomfort with this harsh decision, and eventually the chorus is able to convince Creon to change his mind on the matter.
In this way, Sophocles has given the chorus a unique role in Antigone. While it serves to provide historical and mythological context to the viewer, it also directly intervenes in the central action of the plot.