"What is the keystone?" is a reference to "what is the thing that holds the eye of providence together." The stability of power players working together is inherently unstable. What are the traits required to become hyper successful within the highest echelons? Those traits represent something akin to Satan. Betrayal, ruthlessness, persistence, accumulation of "souls" which is essentially accumulation of "control over others." Think employees, think buy-outs, think threat of violence.

So considering the above, how do comparable power players work together to further their interest without destruction of each other? The answer is, at the root, mutual blackmail. If you're powerful and about to sign a deal with another powerful person, sealing the deal over a horrific deed to ensure compliance by both or destruction by the blackmail...it's something of a power player's mutual assured destruction. Now if you can believe that this is possible, you must logically carry it to it's inevitable conclusion which is propagation. Power players blackmailing with other power players on and on and on.

Something inherent to the psyche of humans is the susceptibility to go along, to work together towards a greater goal (good or evil). That greater goal is something that is encapsulated roughly by an archetype. For example: think about a god of war. A culture's understanding of a good warrior is the result of stories told about the SET of warriors, over generations. Those stories meld together to form a singular archetype. That archetype encapsulates the greatest, most important traits that the culture deems fit for it's warriors. It's towards that archetype that all young people are driven by the collective mind because the collective mind deems it an important role in their culture. It's the parring down of multiple 'heros' of a culture into a singular metaphorical ideal. So it's easy to imagine that all traits of human culture can be represented in this manner. This is how we, as humans, generate a polytheistic religion where the ideals created by generations past informs the future generations.

So considering the above, the next line in Q's statement is "Is Satan real?" The statement is to say: "Is satan a physical being of omnipotent power manifested in the actual physical world?" To that, considering the above, the answer is resoundingly.

Q's next line that says "does the 'thought of satan exist?" The statement is to say: "Does there exist a metaphysical idea that propagates through culture over time that represents the idea of Satan as we know it?" The answer is, resoundingly, Yes.

Finally, "Who worships Satan?" Or put another way: Who worships the IDEA of Satan as we established just now? Well, it's those powerful people who rely on the "idea of Satan," derived from ritualized blackmail sessions, to ensure the stability of the hierarchy of power otherwise called the Eye of Providence...These are the people who worship Satan.

This group is otherwise known as "The Cult."

And who controls "The Cult" according to Q?