金剛經纂要刊定記 4.118

4.118

Regarding "originally only, etc.": this explains the cause of the doubt arising. Because practitioners of the two vehicles only take the sixteen-foot physical form to be the true Buddha, taking this form as the fruit, they therefore do not believe in the cause of non-abiding, because cause and fruit are not of the same kind. Now the Buddha raises the fruit to question him, enabling him to know that the ocean of the fruit is markless, so that naturally he will have no doubt regarding the cause of non-abiding.