大方廣圓覺修多羅了義經略疏 2.727

2.727

謂由執四相為實我體，所以於自生愛、於他生憎，順我者愛、違我者憎。如是愛憎皆由執我，故曰由此。

This means that because they grasp the four marks as the entity of a real self, they generate love toward themselves and hatred toward others; they love whatever accords with the self and hate whatever opposes the self. Such love and hatred both arise from grasping onto a self; hence it says 'thereby'.