وَمِنهُم مَّن يُوْمِنُ بِهِAnd of them there are some who believe therein;means that among those you were sent to, O Muhammad, are people who will believe in this Qur'an, follow you and benefit from what has been sent to you.وَمِنْهُم مَّن لاَّ يُوْمِنُ بِهِand of them there are some who believe not therein,but dies as a disbeliever and will be resurrected as such.وَرَبُّكَ أَعْلَمُ بِالْمُفْسِدِينَAnd your Lord is All-Aware of the mischief makers.He best knows those who deserve guidance, so He guides them, and those who deserve to go astray, He allows to go astray.Allah is, however, the Just who is never unjust. He gives everyone what they deserve. All Glory is His, the Exalted. There is no God but He