Finer Skill Control.
One of the more complicated things about using magical skills and spells, was controlling the way the skills and or spells were executed.
There existed and infinite number of possible ways under the sun for mana to be applied, so each individual was unique in their own right when it came to creating and using their respective skills and spells.
Cain's skill, {Divine Essence of Metallurgy} had evolved from two lesser skills; {Metal Manipulation} and {Metal Creation}.
Both skills, were in essence, mediums for him to exert his control over mana and mananrelated phenomena.
{Metal Creation} allowed him to create metallic material with mana, while {Metal Manipulation} gave him the ability to exert his will upon metallic objects, including those he created with {Metal Creation}.
Pulling these two together resulted in the creation of the {Divine Essence of Metallurgy}.