大乘起信論義記 2.264

2.264

初中言無明力者，謂根本無明即所依緣也。明心不自起，起必由緣。不覺心動者，正明起相，釋成業義，起動義是業義故。

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.