大般涅槃經義記 4.207

4.207

下就癈時明無力，先喻、次合。「如蚊子澤不能沾洽眾生心地」下乘明其法滅盡相，此經先滅當處不行名沒於地，「當知」已下明此滅時餘經悉滅。

Below, it clarifies [the sūtra's] lack of efficacy according to the time of decline, first with an analogy, then the application. From "Just as a mosquito's oil cannot moisten the mind-ground of sentient beings" onward, it takes the opportunity to clarify the marks of the complete extinction of the Dharma. This sūtra being the first to be extinguished and no longer circulating in that place is called "sinking into the earth." From "You should know..." onward clarifies that when this [sūtra] is extinguished, all the other sūtras will be extinguished as well.