John 12:40

"He hath blinded their eyes, and hardened their heart; lest they should see with their eyes, and understand with their heart, and turn from their ways, and I should heal them."

Romans 9:18-20

So then he hath mercy on whom he will, and hardeneth whom he will.

2 Thessalonians 2:11-12

And for this cause God sendeth them a working of delusion, that they may believe the falsehood;

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 cause God sendeth them a working of delusion, that they may believe the falsehood;

And hardened

John 12:40
"He hath blinded their eyes, and hardened their heart; lest they should see with their eyes, and understand with their heart, and turn from their ways, and I should heal them."
Romans 9:18
So then he hath mercy on whom he will, and hardeneth whom he will.