This is me like a mufukka LMAO! I'm so fukking confused, but I love this show
They explained this in one of the episodes? That makes a lot of sense now
They never gave us a full explanation ep or dialog more like they drip feed it throughout both seasons. The cards are in ancient mythriac they keep finding them, they found cave paintings in s1 that depicted a spaceship that looks just like mythriac ships leaving Kepler for earth. They talked about the mythriac bible having hidden technology formulas and so on in them, which is how they built necromancers and spaceships (thats why mythriacs have all the fancy clean tech). They still don't fully understand it either.
This is why I think Mother taking the caul from Grandmother probably gonna end up fukking her/them over. She says she's a shepherd and implied she's not a weapon but who knows...she was looking kinda sinister in that preview. If the caul was a "filter" there must have been a reason why they put it on her in the first place. I bet it's gonna be some kind of limiter.