﴿ ذَٰلِكَ بِأَنَّهُمْ ءَامَنُوا۟ ثُمَّ كَفَرُوا۟ فَطُبِعَ عَلَىٰ قُلُوبِهِمْ فَهُمْ لَا يَفْقَهُونَ ﴾

“this, because [they profess that] they have attained to faith, whereas [inwardly] they deny the truth - and so, a seal has been set on their hearts so that they can no longer understand [what is true and what false].”

Please check ayah 63:4 for complete tafsir.