Mark 4:12

that they may surely see, and not perceive; and that they may surely hear, and not understand; lest they should turn to me, and their sins should be forgiven them.

Matthew 13:14-15

And in them is fulfilled the prophesy of Isaiah, which says: You shall surely hear, and you will not understand; and you shall surely see, and you will not perceive.

Luke 8:10

He replied: To you it is given to know the mysteries of the kingdom of God: but to others in parables; that when they see, they may not see, and when they hear, they may not understand.

John 12:37-41

But though he had done so many signs in their presence, yet they believed not on him,

Acts 3:19

Repent, therefore, and turn, in order that your sins may be blotted out, so that seasons of refreshing may come from the presence of the Lord,

Acts 28:25-27

And not agreeing among themselves, they departed, after Paul had spoken one word: Well did the Holy Spirit speak to our fathers by Isaiah the prophet,

Romans 11:8-10

as it is written: God has given them a spirit of stupor, eyes with which they can not see, and ears with which they can not hear.

2 Timothy 2:25

in meekness instructing those who oppose themselves, if, possibly, God may give them repentance in order to the acknowledgment of the truth,

Hebrews 6:6

if they fall away; since they again crucify in themselves the Son of God, and put him to an open shame.

Treasury of Scripture Knowledge

Summary

That seeing they may see, and not perceive; and hearing they may hear, and not understand; lest at any time they should be converted, and their sins should be forgiven them.

Bible References

That seeing

Matthew 13:14
And in them is fulfilled the prophesy of Isaiah, which says: You shall surely hear, and you will not understand; and you shall surely see, and you will not perceive.
Luke 8:10
He replied: To you it is given to know the mysteries of the kingdom of God: but to others in parables; that when they see, they may not see, and when they hear, they may not understand.
John 12:37
But though he had done so many signs in their presence, yet they believed not on him,
Acts 28:25
And not agreeing among themselves, they departed, after Paul had spoken one word: Well did the Holy Spirit speak to our fathers by Isaiah the prophet,
Romans 11:8
as it is written: God has given them a spirit of stupor, eyes with which they can not see, and ears with which they can not hear.

Be converted

Acts 3:19
Repent, therefore, and turn, in order that your sins may be blotted out, so that seasons of refreshing may come from the presence of the Lord,
2 Timothy 2:25
in meekness instructing those who oppose themselves, if, possibly, God may give them repentance in order to the acknowledgment of the truth,
Hebrews 6:6
if they fall away; since they again crucify in themselves the Son of God, and put him to an open shame.