成唯識論了義燈 7.215

7.215

Question: Regarding the four unhindered knowledges, why are the first three together one obstruction, while the fourth alone is one obstruction? Answer: Although the first three unhindered knowledges have three essences, each has one cognitive object and does not possess multiple understandings. The fourth has a single essence, but its understandings and activities are divided into many, namely the seven elocutions. Also, it is said: The first three are causes and the fourth is a fruit; therefore there is a difference between three and one obstruction.