It can be used only once, what indicates that the consequences of using it are profound. Something that can’t be undone.
Merlin, Cayleb et al. can’t risk to use it. So in the normal cause of action we won’t know what is in it until there are enough Federation level scientist to understand and neutralize what is beneath the temple. Say in a century or two.
But what if a Rakurai spy steals it in Tellersberg and brings it to his boss, our beloved arch villain Clyntahn? After some research the meaning of the key is found and the hidden room in the basement unlocked. There Clyntahn comes eye in eye with his favorite archangel.
After hearing that, if the church is really in dire straits, Schueler can help to solve the problem Clyntahn is overjoyed. He can’t wait to activate the key.
And Schueler appears again. He asks if the church is really in danger, is there no other way out of this crises? Clyntahn gets visions of Charis turned into another Armageddon reef, of heretics all over Safehold drowned in boiling oil and struck down by lighting. And Clyntahn convinces Schueler that they need his help and that they need it know.
“Okay, this is what I build the Temple for. Get everybody and all their stuff out of the Temple. When the Temple is completely evacuated, close the doors and let the rest to me.”
When, after some hours off frantic movement of people and furniture, Clyntahn closes the last Temple door he sees the Square of Martyrs filled with people. Everyone looking up to the top of the Temple dome. Where, like in the old days, a brilliant light calls everybody together to prepare for the visit of an archangel.
The front of the Temple changes into one giant screen. It disappears and in its place there is the image of a man. As big as the Temple itself.
“I am Schueler. I have been called because the Church of God Awaiting can’t survive without my help. I have seen this day coming. It was inevitable. It means Langhorne’s lie has outlived itself.”
Imagine the reaction from the crowd to this announcement.
Schueler continues with the story of Earth and the Gbaba. With images off the old home world of humanity, the spaceships and the colonies. And finally with operation Ark. What should have happened and how Langhorne perverted it. The true story of Shan-Wei and how he decided to wait for this day. How his opponents in the war of the fallen tried to discredit him with the publication of the Book of Schueler. He could not retract it, but he did not think any clergy man would ever be so mad and sick to think of practicing the horrors described in it.
(Anyone imagining Clyntahn's face?)
Schueler declares that from this day on the Temple will be known as The Temple of Knowledge. The library and study rooms making available all the knowledge off old earth to everyone.
And as he finishes the doors open again to a completely revamped Temple. Gone are the religious artifacts and images of the archangels. In its place are desks and consoles for those hungry to learn.
I know this borders on fanfic, but to me it is the best way to describe my speculation what the Key really is.
