all martial skills come from different laws and to achieve a martial skill you have to have affinity for its corresponding laws or law
for example if you are proficient in fire and sword law you can get fire and sword skills or a mixture of both.
Many skills can be similar to each other but have completely varying degree of effects.
as the cultivator becomes proficient in a law he has a chance of getting a hang of complicated skills. so you have to have god understanding of laws as well as cultivation.
a cultivator of high cultivation stage will not get good skills if his law proficiency is low.and vice versa.
a teachers main reason to exist in the story is to gelp its student shape their law and cultivation.