大乘起信論義記 2.111

2.111

In the former part, regarding "awakens to the source of the mind": the source of the defiled mind refers to the purity of nature; also, the source of coarse marks refers to the mark of arising. When the path of incipient enlightenment is perfected, it is identical with innate enlightenment, hence it is said to be "ultimate"; this is at the stage of Buddhahood. Because one has not fully comprehended its source and incipient has not yet become identical with innate, it is said to be "not ultimate"; this is at the diamond-like [samādhi] and below.