大般涅槃經義記 8.164

8.164

法中，初先開列四門，下牒辯釋。「因」牒初門，「即十二緣」斥其體相。十二緣法，近生觀智，遠為涅槃正因種子，故名為因。

In the doctrine, first the four gates are laid out, and below they are taken up to be distinguished and explained. "Cause" takes up the first gate, and "is the twelve links" identifies its substantial characteristic. The dharma of the twelve links proximately produces contemplative wisdom and distantly serves as the seed of the direct cause of nirvāṇa, and hence is called a cause.