仁王經疏 2.465

2.465

釋曰：自下第二明理性智母。謂諸因位真如佛性，能顯法身本覺智果，故言性根本智母，即是正因；若望受用，即是依因。

The commentary states: From here below, the second part explains the mother of wisdom of principle-nature. That is to say, the tathatā buddha-nature in the various causal stages can reveal the fruit of original awakening wisdom of the dharmakāya; hence it is called "the root mother of wisdom of nature," which is the primary cause (*hetu*); if viewed in relation to the enjoyment [body], it is the reliant cause.