Amatul Rahmân Omer:
And We have placed barriers (of their stubbornness rendering them unable to look forward to the bright future of Islam and rise to eminence by accepting it) in front of them, and barriers (of their prejudices) behind them (thus rendering them unable to look back at the doom of those who rejected the truth in the past). Thus We have kept them behind the veil so that they cannot see (so have become totally devoid of spiritual light).