大乘起信論義記 2.240

2.240

In the application, "the untainted" refers to the two kinds of enlightenment, incipient and innate. "Avidyā" refers to fundamental and derivative non-enlightenment. Both of these have karmic functioning and manifestation without being truly real; hence they are called "karmic illusions." These correspond to the various vessels. "All share the nature and marks of tathatā" means: because the gate of tathatā is stirred to become these two dharmas of defilement and purity in the gate of arising and ceasing, with no separate substance, it says "nature." Tathatā also takes these two dharmas as its marks; its pure mark can be understood. As for its defiled mark, the text below says: "It is only because of the perfuming of avidyā that there are defiled marks."