Everyone knew that the Emperor sat on the Golden Throne, no one knew what he was doing on the throne.
For ten thousand years, the death of every loyalist has recharged the Golden Throne. The Inquisition said this was faith, and the National Religion said it was sacrifice. It was wrong, he was plundering. He used faith as a hook to hook every soul that died for him, peeling off the core terms from it, and saved it for ten thousand years. Not for eternal life, not for divine power, but for when the end comes, to reach into the subspace, unscrew the shell of the four evil gods, and redefine them.
Slaanesh rules pleasure? Change it to the ecstasy of creation, with Tzeentch in charge of subterfuge? Change to the possibility of change, Nurgle rules decay? Change it to a cycle of life and death. Khorne rules the killing? Changed to Protective Fury.
Then plunder yourself, return the master of mankind to mankind, return the golden majesty to the air, and leave the silent watch on the empty throne. From now on, no one makes choices for humans.