首楞嚴義疏注經 8.159

8.159

一中現無量，故云於同現異。無量中現一，故云異相見同。身說皆然也。以知一切法同一法性，能作種種異說，而不失一性一相之旨。《維摩》云「能善分別諸法相，於第一義而不動。」故名善現。

Manifesting the immeasurable within the one is why it says 'revealing differences within sameness.' Manifesting the one within the immeasurable is why it says 'seeing sameness within different characteristics.' This is true of both physical form and preaching. Because he knows that all dharmas share the same Dharma-nature, he can make all kinds of diverse expositions without losing the purport of the single nature and single characteristic. The Vimalakīrti states: 'Being well able to distinguish all characteristics of dharmas, yet unmoved in the primary truth.' Hence it is called 'skillful manifestation.'