Arbit is a Divine built by Grand Magnificent, designed to be wildly unpredictable enough that Crystal Palace would be thrown off by it and cease to be able to make predictions.
Bit by bit, Grand Magnificent would become the excerpt of Arbit and devote his life to it.
The Divine was likened to a Double Pendulum & a washing machine with a brick inside of it bouncing on a trampoline in terms of its unpredictability.
Notes
Grand Magnificent, at first, said that Arbit was not truly a Divine (and called it a random number generator) but that he was only calling it that so people would respect it more. However, as perceptions of what made a Divine a Divine changed and morphed and it took Grand Magnificent on as an excerpt, it is likely that Arbit counts as a 'true' Divine.