大方廣佛華嚴經隨疏演義鈔 33.84

33.84

疏「故遺教經對此明小水長流」者，即是彼經八大人覺中釋精進相。經云「汝等比丘若勤精進，則事無難者。是故汝等當勤精進。譬如小水常流，即能穿石。若行者之心數數懈廢，譬如鑽火，未熱而息。雖欲得火，火難可得。是名精進。」釋曰：彼以鑽火數息以況懈怠，小水長流以比精進，故云對此名小水長流。

Regarding the commentary's phrase "Therefore, the Sūtra of the Buddha's Last Teaching, contrasting with this, explains that a small stream of water flows continuously": this is the explanation of the characteristic of vigor among the eight realizations of great beings in that sūtra. The sūtra says: "O monks, if you are diligently vigorous, then nothing will be difficult. Therefore you must be diligently vigorous. It is like a small stream of water constantly flowing, which is able to bore through rock. If a practitioner's mind frequently becomes lax and remiss, it is like drilling for fire and resting before it is hot: though one desires to obtain fire, fire is hard to obtain. This is called vigor." Exegesis: That text uses resting repeatedly when drilling for fire to illustrate indolence, and a small stream of water flowing continuously to illustrate vigor; hence it says that contrasting with this, it speaks of a small stream of water flowing continuously.