إِنْ هُوَ (It is): The Holy Qur’an. It is a reminder for all mankind.

 ذِكْرٌ (a reminder): Points out to the instinct of faith of upon which Allah (swt) has created all people; because the reminder means there is something you used to have but you forgot it so that someone came to remind you of it. That is because, originally, all humans received Allah’s (swt) method through Adam (pbuh).