Kluster has hidden the truth about Zelhart being Gremory and that he left the Kingdom, but recently after hearing the Oracle's plan, he decided to tell the high ranks from the Blood Temple.
Even though the Kingdom and the cult are based on lies, this time the truth was necessary because they need to be ready, so all the ranks S from Viridian were aware that Zelhart is the enemy and who he is.
Including Adel, Ramses, and his mages too. Their faith only got strong than ever once they heard about creating a Rebis.
The Magnum Opus will simply turn the world upside down, armies will not matter anymore once they acquire the Rebis. All the ancient legends found in dungeons said about Rebis as if every time something important and remarkable happened, a Rebis was there.