Berlin talks about the significance of the mask and it's underlying theme in the play.

The Great God Brown (written 1925, produced 1926) is O'Neil's first play of the late twenties, and the last play to be produced by the triumvirate of Kenneth Macgowan, Robert Edmond Jones, and O'Neill, thereby ending their five-year association. The play mystified its audience because of O'Neill's complex use of masks, but managed to please many reviewers, even those who found the play puzzling, and ran for 283 performances. Because the audiences and reviewers did not understand the play, O'Neill presented many comments on the play's meaning, explaining what he intended to accomplish. The gap between his intentions and the play's accomplishment is very wide indeed, and the reasons for this gap are not difficult to discern.

O'Neill's use of the mask, the play's most important dramatic device, became a kind of 'cause' for O'Neill...