Caution: Translations of Quran and Ḥadīth may lead to possible misapplications and misinterpretations. This site is intended for students of sacred knowledge that are proficient in comprehending classical Arabic and have a strong foundation in Islamic sciences. Also note that religious injunctions rely on several aspects beyond what one may glean through reading individual aḥādīth.
quran:36:9

And We have put before them a barrier and behind them a barrier and covered them, so they do not see.  

And We have set before them a barrier (read saddan or suddan in both instances) and behind them a barrier; so We have covered them, so they do not see — this is also figurative, depicting the way in which the paths of faith are closed to them.
القرآن:٣٦:٩

وَجَعَلْنَا مِنْ بَيْنِ أَيْدِيهِمْ سَدًّا وَمِنْ خَلْفِهِمْ سَدًّا فَأَغْشَيْنَاهُمْ فَهُمْ لَا يُبْصِرُونَ  

{وجعلنا من بين أيديهم سدا ومن خلفهم سدا} بفتح السين وضمها في الموضعين {فأغشيناهم فهم لا يبصرون} تمثيل أيضا لسدّ طرق الإيمان عليهم.