妙法蓮華經玄義 2.21

2.21

如是體者，攬彼摧折，麁惡色、心，以為體質也。復次，此世先已摧心，來世摧色。又此世華報，亦摧色、心，來世果報亦摧色、心。故以被摧色、心為體也。

As for 'such substance', it takes that crushed, coarse and evil form and mind as its physical substance. Furthermore, in the present lifetime it has already crushed the mind, and in the future lifetime it will crush the form. Again, in the present lifetime the flower-reward also crushes form and mind, and in the future lifetime the fruit-retribution also crushes form and mind. Therefore it takes the crushed form and mind as its substance.