"Spatial skills… you will be learning to manipulate spatial mana at some point, correct? Can you make scrolls with it? This spatial skill? Can you show others how to use it?" Mordant has keeping a highly focused gaze on Walker. He wanted to be able to learn these things. He wanted to be able to do more.
The reason that this was such a focus wasn't just the rarity and strength of skills. But also the fact that light and darkness mana were related to space in a way. Light could take up space and could be thought of as a unique mana that interacted with space differently than all other manas.
Shadows and darkness were different. The darkness mana was odd already but everyone has seen that some monsters could use shadows to hide themselves. Some systems even came with skills that let others become one with shadows and travel. Therefore, it was clear that shadows and darkness already interacted with space in some form or fashion.