ذٰلِكَ بِاَنَّهُمۡ اٰمَنُوۡا ثُمَّ كَفَرُوۡا فَطُبِعَ عَلٰي قُلُوۡبِهِمۡ فَهُمۡ لَا يَفۡقَهُوۡنَ

That is because they believed, and then they disbelieved; so their hearts were sealed over, and they do not understand