Moana personally led the Light Priests to the Heavenly Radiance Plane to pray and begin the Holy Light ritual.
The Goddess of Light answered the Light Priests' prayers. Holy Light descended, transforming the Heavenly Radiance Plane into the Divine Grace Plane.
The people of the Light Territory in the Divine Grace Plane of Light couldn't take part in plane wars.
Medivh didn't mind. He wasn't short on soldiers.
As long as he could gain the Church of Light's approval, it was worth it.
It would be even better if the people of the Heavenly Radiance Plane approved of him, were willing to carry out the Living History Project, practice the Bone Knight Secret Art, and donate their remains after death to be turned into Holy Light Skeletons.
There wasn't much resistance to this, actually. The people of the Wrynn Family were loyal to Medivh and willing to donate their bodies after death to become the skeletons of their ancestors.
The Church of Light recognized Holy Light Skeletons as believers. Turning into Holy Light Skeletons after death didn't violate its doctrines.
It all depended on whether the believers who had moved over from the other Domains of Light were willing to donate their remains and become Holy Light Skeletons.
Medivh thought there was a lot of potential in this.
They were all Children of Light. When those believers saw the people of the Wrynn Family donate their remains and worship the Goddess of Light eternally as Holy Light Skeletons, they would surely follow suit to prove their own devotion.
Skeletons were somewhat unsightly, so Medivh thought it over and suggested to the Church of Light that Holy Light Skeletons transformed with their memories intact be called Holy Light Heroic Spirits.
The Church of Light accepted his suggestion. From then on, the