大般涅槃經義記 6.85

6.85

初復次中，「無所得者名四無礙」當相正辯，菩薩無礙證實方成，證實離相故名無得。「何以故」下破遣有得，成前無得。「何故」徵問。下對顯之，得名為礙，礙名四倒，反舉有得。情取名得，得妨實慧，故名為礙。礙是常樂我淨四倒，故復指之。「菩薩無倒，故得無礙」破得顯無。「是故」下結。

In the first reiteration, "That which has nothing attained is called the four unobstructed knowledges" directly explains it according to its characteristics: a bodhisattva's unobstructedness is accomplished only upon realizing reality, and realizing reality is free from marks, hence it is called non-attainment. From "Why is this?" onward, it refutes and dispels having attainment to establish the aforementioned non-attainment. "Why?" raises the query. Below, it responds to reveal it: attainment is called obstruction, and obstruction is called the four inversions; it conversely cites having attainment. Grasping with sentiment is called attainment, and attainment hinders true wisdom, hence it is called obstruction. Obstruction is the four inversions of permanence, bliss, self, and purity, which is why he points to them again. "The bodhisattva is without inversions and therefore attains unobstructedness" refutes attainment to reveal non-attainment. From "Therefore" onward, it concludes.