大方廣圓覺修多羅了義經略疏 2.264

2.264

麁念既盡，得少輕安，於彼淨時心生愛著。於淨起解，名為淨解。繫心在淨，故成障礙。非外塵所擾，故言自礙。

When coarse thoughts are exhausted, one attains a little light ease, and one gives rise to attachment toward that purity. Generating an understanding regarding purity is called an "understanding of purity." Because one ties one's mind to purity, it becomes an obstruction. Since it is not disturbed by external defilements, it is said to be "one's own obstruction."