大乘起信論裂網疏 4.38

4.38

無明厚，則信心難生。無明薄，則信心易發。煩惱厚則難斷，煩惱薄則易除。而無明、煩惱又各有界外、界內之不同，故唯如來能盡知也。

When ignorance is thick, faith is difficult to generate. When ignorance is thin, faith easily arises. When afflictions are thick, they are difficult to sever; when afflictions are thin, they are easily eliminated. Moreover, ignorance and afflictions each have the differences of being outside the realm [of samsara] and inside the realm, so only the Tathāgata is able to know them exhaustively.