首楞嚴義疏注經 8.314

8.314

愛染之情正是眾生生死根本，名為內分，分亦因義。情愛沈下，能潤業受生，故如水也。外由內感，故有水輪遍十方界。

The emotion of love and defilement is precisely the root of sentient beings' birth and death; it is named the 'internal share.' 'Share' (fen) also has the meaning of 'cause.' Emotion and love sink downward and can moisten karma to receive rebirth, so they are like water. The external is resonated by the internal, which is why there is the water-wheel pervading the worlds of the ten directions.