Mark 4:12

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

Then he said, Go and tell this people, Hear indeed, but do not understand; and see indeed, but do not perceive.

Jeremiah 5:21

Hear now this, O foolish people and without heart, who have eyes and do not see; who have ears, and do not hear:

Deuteronomy 29:4

Yet the LORD 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 bemoaning himself thus, Thou hast afflicted me, and I was chastised as an indomitable bullock: turn thou me, and I shall be turned; for thou art the LORD my God.

Matthew 13:14-15

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

Luke 8:10

And he said, Unto you it is given to know the mysteries of the kingdom of God, but to the others in parables that seeing they might not see and hearing they might not understand.

Isaiah 44:18

They did not know nor understand; for he has anointed their eyes that they not see and their hearts that they not understand.

Ezekiel 12:2

Son of man, thou dwellest in the midst of a rebellious house, which have eyes to see and do not see; they have ears to hear and do not hear; for they are a rebellious house.

Ezekiel 18:27-32

Again, when the wicked man leaves his wickedness that he has committed and lives according to judgment and righteousness, he shall cause his soul to live.

John 12:37-41

But although he had done so many signs before them, yet they did not believe in him,

Acts 3:19

Repent ye therefore and be converted that your sins may be blotted out, for the times of refreshing of the presence of the Lord are come;

Acts 28:25-27

And when they did not agree among themselves, they departed, after Paul had spoken this word, Well spoke the Holy Spirit by Isaiah the prophet unto our fathers,

Romans 11:8-10

(according as it is written, God has given them the spirit of anguish, eyes with which they do not see and ears with which they do not hear) unto this day.

2 Timothy 2:25

that with meekness they might teach those that resist, if God peradventure will grant unto them that they might repent and know the truth,

Hebrews 6:6

and have backslidden, be renewed again by repentance, crucifying again for themselves the Son of God and putting 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 the LORD has not given you a heart to perceive and eyes to see and ears to hear until today.
Isaiah 6:9
Then he said, Go and tell this people, Hear indeed, but do not understand; and see indeed, but do not perceive.
Isaiah 44:18
They did not know nor understand; for he has anointed their eyes that they not see and their hearts that they not understand.
Jeremiah 5:21
Hear now this, O foolish people and without heart, who have eyes and do not see; who have ears, and do not hear:
Matthew 13:14
And in them is fulfilled the prophecy of Isaiah, which says, By hearing ye shall hear and shall not understand, and seeing ye shall see and shall not perceive;
Luke 8:10
And he said, Unto you it is given to know the mysteries of the kingdom of God, but to the others in parables that seeing they might not see and hearing they might not understand.
John 12:37
But although he had done so many signs before them, yet they did not believe in him,
Acts 28:25
And when they did not agree among themselves, they departed, after Paul had spoken this word, Well spoke the Holy Spirit by Isaiah the prophet unto our fathers,
Romans 11:8
(according as it is written, God has given them the spirit of anguish, eyes with which they do not see and ears with which they do not hear) unto this day.

Be converted

Jeremiah 31:18
I have surely heard Ephraim bemoaning himself thus, Thou hast afflicted me, and I was chastised as an indomitable bullock: turn thou me, and I shall be turned; for thou art the LORD my God.
Ezekiel 18:27
Again, when the wicked man leaves his wickedness that he has committed and lives according to judgment and righteousness, he shall cause his soul to live.
Acts 3:19
Repent ye therefore and be converted that your sins may be blotted out, for the times of refreshing of the presence of the Lord are come;
2 Timothy 2:25
that with meekness they might teach those that resist, if God peradventure will grant unto them that they might repent and know the truth,
Hebrews 6:6
and have backslidden, be renewed again by repentance, crucifying again for themselves the Son of God and putting him to an open shame.

General references

Proverbs 28:5
Evil men do not understand judgment, but those that seek the LORD understand all things.