John 12:40

He has blinded their eyes, and hardened their heart, lest they should see with their eyes, and understand with their heart, and should turn, and I should give them health.

Romans 9:18-20

Therefore, he has mercy on whom he wills to have mercy: and whom he wills to harden, he hardens.

2 Thessalonians 2:11-12

And for this reason God will send them strong delusion, in order that they may believe a lie,

Treasury of Scripture Knowledge

Summary

O LORD, why hast thou made us to err from thy ways, and hardened our heart from thy fear? Return for thy servants' sake, the tribes of thine inheritance.

And hardened

Bible References

Why

2 Thessalonians 2:11
And for this reason God will send them strong delusion, in order that they may believe a lie,

And hardened

John 12:40
He has blinded their eyes, and hardened their heart, lest they should see with their eyes, and understand with their heart, and should turn, and I should give them health.
Romans 9:18
Therefore, he has mercy on whom he wills to have mercy: and whom he wills to harden, he hardens.