This richly decorated chamber contains the massive carving of the face of Baphomet, the avatar of Tobias. Upon entering, he will effectively order you to take the right-hand door, to lead you to the grail. Geffrye will appear and ask for you to reconsider and suggest and alternative, more dangerous route through the abandoned Malik's lab, which is free of Malik's machinations.
This is the place where the plot branches and you can follow either Geffrye's route or Tobias'. Geffrye's route all but guarantees the good ending, while Tobias' path can lead to two bad endings and one good one (best, if you want to spare Geffrye).