大方廣佛華嚴經隨疏演義鈔 60.108

60.108

疏「由俱不住」下，疏釋論也。論云「菩薩至涅槃城不復退還，而能利益眾生，得世間出世間勝事。」疏釋意云：由不住涅槃，能入世間；由不住生死，能出世間。此二無礙，即是勝事，勝事即無住涅槃故。無住涅槃，唯佛方得，名為勝事。

Regarding the commentary's "Because of not abiding in either" and below: the commentary explains the treatise. The treatise says: "The bodhisattva reaches the city of nirvāṇa and never regresses, yet is able to benefit sentient beings and attain the superior matters of the mundane and supramundane." The commentary's intention in explaining is: because of not abiding in nirvāṇa, one can enter the mundane; because of not abiding in saṃsāra, one can transcend the mundane. These two being unhindered is precisely the "superior matter"; and the superior matter is non-abiding nirvāṇa. Non-abiding nirvāṇa is attained only by a Buddha, hence it is called a "superior matter."