起信論疏筆削記 1.39

1.39

水無下二句，喻生滅不礙真如。初句反顯，以喻真如門中無有異染淨之一心也，故云水無等。次句順喻，由不異故，遂能即彼生滅而顯真如，故云即波等。此喻前文不捨緣而即真，凡聖致一也。

The two lines from "Water has no..." onwards illustrate that arising and ceasing do not obstruct tathatā. The first line reveals [the meaning] by negation, in order to illustrate that within the gate of tathatā there is no One Mind distinct from defilement and purity; hence it says "water has no [wetness apart from waves]," and so on. The next line is the direct simile: because they are not different, one is able to reveal tathatā right within that arising and ceasing; hence it says "directly upon the waves," and so forth. This illustrates the previous text's point that without abandoning conditions it is directly real, and ordinary beings and sages reach unity.