大方廣佛華嚴經疏 6.20

6.20

四中，知世間法者，謂眾生世間心法各異，知已隨宜現通說法，故云安立。一念速安，非人天外道所能思議。以此莊嚴如來教海，此於安立教法，遲鈍障得解脫也。

In the fourth, "knowing the dharmas of the world" means that the mental dharmas of the sentient world are each different; having known them, he manifests spiritual penetrations and expounds the Dharma as appropriate, hence it is called "establishing." Establishing swiftly in a single thought is beyond the comprehension of humans, devas, or non-Buddhists. Using this to adorn the Tathāgata's ocean of teachings is obtaining liberation from the obstruction of sluggishness in establishing the teachings of the Dharma.