大乘義章 16.58

16.58

次分止觀。定覺是止，猗捨助成；擇法是觀，精進及喜二法助成；念則俱調。問曰：於八正道中精進通策，何故此中念則俱調？釋言：互從。理亦應齊，但諸行門義意各異。八正見道，見道速疾，精進之心於速力強，故用通策。七覺修道，修道容裕，止觀須等，念能俱調，是故用之通調止觀（此三門竟）。

Next is distinguishing śamatha and vipaśyanā. The awakening factor of samādhi is śamatha, assisted and completed by pliancy and upekṣā; investigation of dharmas is vipaśyanā, assisted and completed by the two factors of vigor and joy; while mindfulness regulates both. Question: In the eightfold noble path, vigor universally urges them on; why here does mindfulness regulate both? Explanation: They mutually follow each other. In principle they should also be equivalent, but the meaning and purport in the various approaches to practice each differ. The eightfold noble [path] is the path of vision; the path of vision is swift, and the mind of vigor has great power in swiftness, so it is used to universally urge them on. The seven factors of awakening are the path of cultivation; the path of cultivation is relaxed and broad, where śamatha and vipaśyanā must be equal, and mindfulness can regulate both; therefore it is used to universally regulate śamatha and vipaśyanā (this concludes the third gate).