大般涅槃經義記 8.158

8.158

上來辯中，下明眾生不見佛性故無中道。「佛性雖常，為無明覆，不能得見」明凡不見。「又未能度十二緣」等明小不見，初先法說，次以喻顯。二乘觀法未能及實，故如兔、馬不得水底。「何以」下釋，以凡二乘不見佛性，故能觀智不名中道。

The preceding [passage] explained the middle; below it is clarified that sentient beings do not see the buddha-nature and therefore lack the middle way. "Although the buddha-nature is permanent, covered by ignorance they cannot see it" explains that ordinary beings do not see it. "Furthermore, they have not yet been able to cross the twelve links of dependent origination," and so forth, explains that the Hīnayāna does not see it: first it is explained via doctrine, and next it is revealed via an analogy. The two vehicles' contemplation of phenomena has not yet been able to reach reality, and hence they are like the rabbit and the horse that cannot reach the bottom of the water. "Why?" and below explains it: because ordinary beings and the two vehicles do not see the buddha-nature, the wisdom capable of contemplation is not called the middle way.