大乘起信論別記 1.94

1.94

「覺則不動」者，是反釋。如得始覺時永無動，當知今動只由不覺。

As for "when there is enlightenment, then there is no motion," this is an inverse explanation. Just as when attaining actualized enlightenment there is forever no motion, one should know that motion at present is due solely to non-enlightenment.