Why would a believer be afraid on the Day of Resurrection and at the Bridge (As-Sirat), when he knows that his destiny is Paradise after the bliss of the grave?

The glad tidings that a believer receives in their grave and during the horrors of the Day of Resurrection are part of the general glad tidings for those who are obedient and upright: "So whoever follows My guidance - there will be no fear concerning them, nor will they grieve." (Quran 2:38). Although the horrors of the Resurrection encompass everyone, they are alleviated for the obedient: "The angels will descend upon them, [saying], 'Do not fear and do not grieve but receive good tidings of Paradise, which you were promised.'" (Quran 41:30). The promise of security for the believer is true, but a person does not attain complete certainty of security until they enter Paradise, because the majesty and greatness of Allah awe everyone.