﴿ لِتُنذِرَ قَوْمًۭا مَّآ أُنذِرَ ءَابَآؤُهُمْ فَهُمْ غَٰفِلُونَ ﴾

“[bestowed upon thee] so that thou mayest warn people whose forefathers had not been warned, and who therefore are unaware [of the meaning of right and wrong].”

(That thou mayst warn) by means of the Qur'an (a folk) i.e. the Quraysh (whose fathers were not warned) by any messenger; it is also said that this means: that you may warn your folk as their fathers were warned, (so they are heedless) of the matter of the Hereafter, i.e. they are in denial of it.