妙法蓮華經玄義 4.61

4.61

四天王有，用不動三昧破者，此天守護國土遊行世界，則有果報動，見思、塵沙、無明等動。菩薩修諸行，破諸動，成三昧。誓願熏、機緣感，以本慈悲令他破四動，成三不動，是故名不動三昧。委悉如上說。

As for the existence of the Four Heavenly Kings being destroyed by the unmoving samādhi: these devas guard the realm and roam the world, so there is the motion of retribution, as well as the motions of views and thoughts, of dust and sand, of fundamental ignorance, and so on. The bodhisattva cultivates various practices, destroys these motions, and perfects the samādhi. His vows perfume, the capacities and conditions stimulate, and through his original compassion he causes others to destroy the four motions and perfect the three unmoving states; therefore it is named the unmoving samādhi. The details are as explained above.