"Then you will know" on the Day of Resurrection "who it is that is in clear error," meaning: that you, O polytheists, are the ones in clear error.
﴿فستعلمون﴾ يَوْمَ الْقِيَامَةِ ﴿مَنْ هُوَ فِي ضلال مُبين﴾ أَيْ: أَنَّكُمْ أَيُّهَا الْمُشْرِكُونَ فِي ضلال مُبين.
