金光明最勝王經疏 5.36

5.36

釋名者，自在光潔神用名天。眾天所歸，為君統攝，稱為王也。天之王故，依士釋。方城不同，統領分四，復帶數名。護謂防禦攝養，防禦為彼除災，攝養增其福慧。四天為能護，國者是所護，能所合稱。此廣明彼，名〈四天王護國品〉。

As for explaining the title: Being sovereign, luminous, and possessing spiritual functions is called "heavenly" (deva). Being the refuge of the multitude of devas, ruling and commanding them as their lord, is called "king" (rāja). Because they are kings of heaven, it is explained as a determinative compound (tatpuruṣa). Their directions and citadels differ, their governing is divided into four, and they additionally carry a numerical name. "Protecting" refers to defense and sustenance: defense eliminates calamities for them, and sustenance increases their merit and wisdom. The four heavenly [kings] are the protectors, and the "country" is what is protected; the agent and the object are named together. Because it extensively elucidates this, it is called the "Chapter on the Four Heavenly Kings Protecting the Country."