ذَٰلِكَ بِأَنَّهُمْ ءَامَنُوا۟ ثُمَّ كَفَرُوا۟ فَطُبِعَ عَلَىٰ قُلُوبِهِمْ فَهُمْ لَا يَفْقَهُونَ
Zaalika bi annahum aamanoo summa kafaroo fatubi'a 'alaa quloobihim fahum laa yafqahoon
because they professed faith and then rejected it, so their hearts have been sealed and they do not understand.
That is because they believed, then denied — so their hearts were sealed, and they no longer understand.