Morten St George Theory

[Morten St. George]

If that rosette were a standalone image you might be able to pin the story on it as you have, but how does the rest of it fit into your narrative?

From the bonfire of Montségur (in the top right-hand corner of the rosettes page), the Cathar martyrs ascend to the spiritual world (note the streams and funnel pointing away from the field to other parts of the rosettes page). That's my best guess: most of the rosettes folio is intended to depict the spiritual world (or call it paradise or heaven). Note circulating energies and movement from one real to another, note the serenity of the celestial blue color, note the pipes that might reflect organ music. 

Do you have a better idea on how to depict the spiritual world?

Per Cathar beliefs, martyrdom shortly after receiving the sacrament of consolamentum guaranteed them eternal life in the spiritual world, a permanent escape from repeated reincarnations in the material world. That's why two hundred Cathars voluntarily walked onto the wood of the bonfire. They didn't even have to be tied down.