Tafseer Ibn Kathir of AL MUNAAFIQUUN [3]

ذَلِكَ بِأَنَّهُمْ آمَنُوا ثُمَّ كَفَرُوا فَطُبِعَ عَلَى قُلُوبِهِمْ فَهُمْ لَا يَفْقَهُونَ

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