首楞嚴義疏注經 2.106

2.106

如來藏有四義，故以海喻：永絕百非如海甚深，包含萬有如海廣大，無德不備如海珍寶，無法不現如海現影。其體湛寂不與妄染相應，故云澄清，即前甚深義也。百千者，即前廣大義也。不識是元清淨體，故云棄之。只取昏擾擾相以為心性，故云唯認等。全潮大瀛渤澥，皆海之異名也。

The tathāgatagarbha has four meanings, hence it is compared to the sea: forever transcending the hundred negations, like the sea is extremely deep; containing the myriad existents, like the sea is vast; devoid of any virtue it does not possess, like the sea has precious gems; devoid of any dharma it does not manifest, like the sea manifests images. Its substance is serene and still, not associated with defiled falsity; hence it says "clear and still," which is the former meaning of extreme depth. "Hundreds of thousands" is the former meaning of vastness. Not recognizing that it is the originally pure substance, it therefore says "abandoning it." Only taking the turbidly agitated appearance to be the nature of mind, it therefore says "only recognizing," and so forth. "Entire tide," "great ocean," and "seas" are all different names for the sea.