Date- 2 April 2321
Time- 19:54
Location- Sky Blossom City, Guild Association Mall, Warehouse no.234
If you think about it by practicing their active soul control the card apprentices strengthen their soul and their control over it, in return, their accessible soul energy increases. Other than that there was no other benefits to practicing active soul control without the grimoire.
Now the question was, why can a grimoire give such magical abilities to the card apprentice? Where do these powers come from? According to Ann, this power belonged to the world and we gained access to it by forming a contract with the world's will with the grimoire as the medium. But how does that work? Why was there a need to use the grimoire as a medium? Why can we not directly establish a contract with the World's will?