وَجَعَلْنَا عَلَى قُلُوبِهِمْ أَكِنَّةً أَن يَفْقَهُوهُ وَفِي آذَانِهِمْ وَقْرًا وَإِذَا ذَكَرْتَ رَبَّكَ فِي الْقُرْآنِ وَحْدَهُ وَلَّوْا عَلَى أَدْبَارِهِمْ نُفُورًا

and We cast veils on their hearts, lest they should understand it, and a deafness into their ears. When you mention your Lord alone in the Quran, they turn their backs in aversion.