﴿ إِنَّمَا تُنذِرُ مَنِ ٱتَّبَعَ ٱلذِّكْرَ وَخَشِىَ ٱلرَّحْمَٰنَ بِٱلْغَيْبِ ۖ فَبَشِّرْهُ بِمَغْفِرَةٍۢ وَأَجْرٍۢ كَرِيمٍ ﴾

“Thou canst [truly] warn only him who is willing to take the reminder to heart, and who stands in awe of the Most Gracious although He is beyond the reach of human perception: unto such, then, give the glad tiding of [God’s] forgiveness and of a most excellent reward!”

(Thou warnest only) your warning by means of the Qur'an benefits only (him who followeth the Reminder) i.e. the Qur'an and acts upon its teachings, like Abu Bakr and his fellow believers (and feareth the Beneficent in secret) and works for the Beneficent even though he does not see him. (To him bear tidings of forgiveness) of his sins in the life of this world (and a rich reward) and a fair reward in Paradise.