We have worked on a short bit of lore: the subservience.
The subservience is an important part of the game. It is a ritual aiming at extracting the magical essence of a witch, and it kills her in the process. The imperial Cult of the Light uses it both as a terror weapon and a propaganda tool. Here's an extract from one of their sacred texts, Privileges and Sacraments, in the Liber Clarus.
The subservience - The ultimate Sacrament
The most powerful will be able to receive the greatest of sacraments and will become an integral part of the Light.
You whom feelings overwhelm, offer your burden, deliver yourself from your earthly links and become the standard bearer of the Light.
No emotion can equal the ecstasy of subservience and light will give it to you a hundred times. Enter the eternal room, feel the sweet rays filling your mind and the embrace of the sacred yoke cherish you for eternity.
One mystery remains: what are they doing that for? Why not just kill them? You will be able to discover that in one of the narrative arcs ;)