Mark 4:12

so 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.

Isaiah 6:9-10

And He said, Go, and tell this people, You hear indeed, but do not understand; and seeing you see, but do not know.

Jeremiah 5:21

Now hear this, O foolish people and without heart; who have eyes and see not; who have ears and hear not;

Deuteronomy 29:4

Yet Jehovah has not given you a heart to perceive, and eyes to see, and ears to hear, until today.

Jeremiah 31:18-20

I have surely heard Ephraim mourning to himself, saying, You have chastised me, and I was chastised, as a bull not broken in; turn me, and I shall be turned. For You are Jehovah my God.

Matthew 13:14-15

And in them is fulfilled the prophecy of Isaiah which said, "By hearing you shall hear and shall not understand; and seeing you shall see and shall not perceive;

Luke 8:10

And He said, To you it is given to know the mysteries of the kingdom of God. But to others I speak in parables, so that seeing they might not see and hearing they might not understand.

Isaiah 44:18

They have not known nor understood; for He has shut their eyes so that they cannot see; and their hearts so that they cannot understand.

Ezekiel 12:2

Son of man, you dwell in the midst of a rebellious house, who have eyes to see and see not. They have ears to hear and hear not, for they are a rebellious house.

Ezekiel 18:27-32

Again, when the wicked turns away from his wickedness that he has committed and does that which is lawful and righteous, he shall save his soul alive.

John 12:37-41

But though He had done so many miracles before them, yet they did not believe on Him,

Acts 3:19

Therefore repent and convert so that your sins may be blotted out, when the times of refreshing shall come from the presence of the Lord.

Acts 28:25-27

And disagreeing with one another, they were let go, Paul saying one word: Well did the Holy Spirit speak through Isaiah the prophet to our fathers,

Romans 11:8-10

even as it is written, "God gave to them a spirit of slumber, eyes not seeing, and ears not hearing" until this day.

2 Timothy 2:25

in meekness instructing those who oppose, if perhaps God will give them repentance to the acknowledging of the truth,

Hebrews 6:6

and who have fallen away; it is impossible, I say, to renew them again to repentance, since they crucify the Son of God afresh to themselves 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.

General references

Bible References

That seeing

Deuteronomy 29:4
Yet Jehovah has not given you a heart to perceive, and eyes to see, and ears to hear, until today.
Isaiah 6:9
And He said, Go, and tell this people, You hear indeed, but do not understand; and seeing you see, but do not know.
Isaiah 44:18
They have not known nor understood; for He has shut their eyes so that they cannot see; and their hearts so that they cannot understand.
Jeremiah 5:21
Now hear this, O foolish people and without heart; who have eyes and see not; who have ears and hear not;
Matthew 13:14
And in them is fulfilled the prophecy of Isaiah which said, "By hearing you shall hear and shall not understand; and seeing you shall see and shall not perceive;
Luke 8:10
And He said, To you it is given to know the mysteries of the kingdom of God. But to others I speak in parables, so that seeing they might not see and hearing they might not understand.
John 12:37
But though He had done so many miracles before them, yet they did not believe on Him,
Acts 28:25
And disagreeing with one another, they were let go, Paul saying one word: Well did the Holy Spirit speak through Isaiah the prophet to our fathers,
Romans 11:8
even as it is written, "God gave to them a spirit of slumber, eyes not seeing, and ears not hearing" until this day.

Be converted

Jeremiah 31:18
I have surely heard Ephraim mourning to himself, saying, You have chastised me, and I was chastised, as a bull not broken in; turn me, and I shall be turned. For You are Jehovah my God.
Ezekiel 18:27
Again, when the wicked turns away from his wickedness that he has committed and does that which is lawful and righteous, he shall save his soul alive.
Acts 3:19
Therefore repent and convert so that your sins may be blotted out, when the times of refreshing shall come from the presence of the Lord.
2 Timothy 2:25
in meekness instructing those who oppose, if perhaps God will give them repentance to the acknowledging of the truth,
Hebrews 6:6
and who have fallen away; it is impossible, I say, to renew them again to repentance, since they crucify the Son of God afresh to themselves and put Him to an open shame.

General references

Proverbs 28:5
Evil men do not understand judgment; but those who seek Jehovah understand all things.