金光明最勝王經疏 3.141

3.141

贊曰：心淨謂菩提分法，軟謂微細煩惱現行障，即軟煩惱是此淨障。或此煩惱依心王故從主為名，名心軟淨障。

The commentary says: Purity of mind refers to the factors of bodhi (bodhipakṣadharma); 'soft' refers to the active obstacle of subtle afflictions; that is, the soft afflictions are the obstacle to this purity. Or, because these afflictions rely on the mind-king, it is named after the primary one, called the obstacle to the mind's soft purity.