﴿ وَجَعَلْنَا مِنۢ بَيْنِ أَيْدِيهِمْ سَدًّۭا وَمِنْ خَلْفِهِمْ سَدًّۭا فَأَغْشَيْنَٰهُمْ فَهُمْ لَا يُبْصِرُونَ ﴾

“and We have set a barrier before them and a barrier behind them, and We have enshrouded them in veils so that they cannot see:”

Please check ayah 36:12 for complete tafsir.