大方廣圓覺修多羅了義經略疏 2.1419

2.1419

別顯四王。別標三類者，以梵與釋諸佛轉法輪時皆為請主，護世持國，使災害不生，故於總列之外而更別明。

This specifically indicates the Four Heavenly Kings. That three categories are specifically listed is because Brahmā and Śakra are both the requesters when all buddhas turn the wheel of the Dharma, and they protect the world and maintain the country so that disasters do not arise; hence, beyond the collective listing, they are also separately set forth.