金剛經纂要刊定記 5.290

5.290

遮疑經意者。以空生前疑得菩提，是有執；此疑不得菩提，是無執。今則雙遣，故云無實無虛。二執既遣，復何疑無耶？故云遮也。

The meaning of the sūtra's repelling of doubt: Because Subhūti previously doubted the attainment of bodhi, that was an attachment to existence; this doubt about not attaining bodhi is an attachment to non-existence. Now both are dispelled together; hence it says "neither real nor unreal." Since both attachments have been dispelled, what doubt about non-existence could remain? Therefore it is called "repelling."