Rebecca's reason for saying it "couldn't be used" was simple.
Ordinary people had no ability to charge a Magic Array, nor could they control when one started or stopped.
The professional Magic Arrays used by mages and the simple symbols common folk carved into stones were entirely different things. The latter were like picking up a stick by the roadside to use as a crutch, while the former was like building a wheelchair through various technical means. The gap between them was like that between raw materials and industrial products—symbols carved into stone could continuously produce an effect without anyone's involvement. Though weak, they required no skill at all. But a Magic Array... it was a complicated thing that had to operate.
Walking on two legs only required lifting your feet and moving, but if you wanted to reach seventy miles per hour, you at least needed to buy a car, fill it with gas, and get a driver's license. Magic Arrays were the same. They required an infusion of energy and a trained professional with magic-control skills to activate and deactivate them—even the simplest arrays worked that way.
Heti and Rebecca could put aside their status and run to the blacksmith shop to inscribe simple combustion-aiding arrays onto every furnace, but they could not stay there all day, recharging the arrays after every batch of ore while also controlling the Energy Flow of every array.
"If an array is carved onto a furnace, its size is bound to be limited. Even with Aunt Heti's skill, she could probably only inscribe auxiliary arrays of the second tier or below," Rebecca explained earnestly, trying hard to make her expression look more professional. "And an array that small can't recharge itself—a Magic Array capable of drawing in ambient magic power has to