In his 782 treatise “The Diamond Scalpel” (“Jinbei Lun”), Zhanran expounds on the universality of buddha nature. He cites the story in chapters 15 and 16 of the Lotus Sutra to support the inclusiveness and truth of the One Vehicle, “that Śākyamuni treats all equally and without bias,” stating that the Buddha’s previous lives express this and “the eternity of his life-span simply proves this.” Echoing the sutra, Zhanran sees the duration of the inconceivable life span as providing the diversity of skillful means to lead all into the one great vehicle. He then also celebrates the bodhisattvas emerging from underground as giving “their lives to increase the path to enlightenment. First they develop the mind [of enlightenment] and, in the end, they will occupy a [vacant] place. How can there be another way by which we all inherit this?” Zhanran sees the underground bodhisattvas and the omnipresent Śākyamuni of the Lotus Sutra as supporting the single great cause in the One Vehicle, elaborated in chapter 2 of the sutra, to help lead all beings onto the path.

Zhanran especially champions the buddha nature of the land itself, serving as a precursor to Dōgen’s worldview. He maintains that the universal buddha nature “is complete within the bodies of all Buddhas, and one body [completely contains] all bodies. In like fashion, [it is complete within] the response-lands of all Buddhas; one land [completely contains] all lands. Bodies and lands being identical, what can be said about bodies can be said about lands. … [This] is another way of saying that you possess [buddha] nature.”