Ye Futian had already comprehended fire, metal, and earth-elemental noble wills. As such, he was experienced in comprehending noble will, which enabled him to learn its way through its workings. Furthermore, he himself had all manners of Life Spirits corresponding to each element. If he had been able to open up more great ruins in the Holy Road, he would have been able to comprehend greater types of noble wills.
As he had made it out of the Holy Road, the pressure emanated by the holy tablets bearing on his will could have also worked as a kind of power of will, and they each bore different elemental traits. As such, Ye Futian was able to use them to comprehend the power of the noble will.