大乘起信論義記 2.264

2.264

In the first, the phrase "by the power of avidyā" refers to fundamental avidyā, which is the relied-upon condition. It clarifies that the mind does not arise of itself; when it arises, it must do so due to conditions. "The non-enlightened mind is stirred" directly clarifies the mark of its arising, explaining and fulfilling the meaning of karma, because the meaning of being stirred to arise is the meaning of karma.