大乘起信論裂網疏 4.38

4.38

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.