A wall between church and state.
Exactly. And the counter-intuitive aspect of that 'wall', the thing that took us awhile to come to understand, is that limiting the religion's influence in government required limiting government's power over religion.
At first, government leaders thought they could reign in religious power by co-opting it, by asserting state power over religion. But in doing so they merely invited religious leaders, albeit unintentionally, to become part of the government. Ambitious religious leaders were eager to use the power of the state to further their agenda.
The same thing is happening now with economic power. And we're making the same mistakes, assuming we can limit the power of wealth by bringing it under government control. When, in fact, that only amplifies and centralizes the oligarch's power.