Mark 4:12

that "'They may look and look but not see, and listen and listen but not understand, lest perchance they should return and be pardoned.'"

Matthew 13:14-15

And in regard to them the prophecy of Isaiah is receiving signal fulfilment: "'You will hear and hear and by no means understand, and you will look and look and by no means see.

Luke 8:10

"To you," He replied, "it is granted to know the secrets of the Kingdom of God; but all others are taught by parables, in order that they may see and yet not see, and may hear and yet not understand.

John 12:37-41

But though He had performed such great miracles in their presence, they did not believe in Him--

Acts 3:19

Repent, therefore, and reform your lives, so that the record of your sins may be cancelled, and that there may come seasons of revival from the Lord,

Acts 28:25-27

Unable to agree among themselves, they at last left him, but not before Paul had spoken a parting word to them, saying, "Right well did the Holy Spirit say to your forefathers through the Prophet Isaiah:

Romans 11:8-10

And so Scripture says, "God has given them a spirit of drowsiness--eyes to see nothing with and ears to hear nothing with--even until now."

2 Timothy 2:25

He must speak in a gentle tone when correcting the errors of opponents, in the hope that God will at last give them repentance, for them to come to a full knowledge of the truth

Hebrews 6:6

it is impossible, I say, to keep bringing them back to a new repentance, for, to their own undoing, they are repeatedly crucifying the Son of God afresh and exposing Him to 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 regard to them the prophecy of Isaiah is receiving signal fulfilment: "'You will hear and hear and by no means understand, and you will look and look and by no means see.
Luke 8:10
"To you," He replied, "it is granted to know the secrets of the Kingdom of God; but all others are taught by parables, in order that they may see and yet not see, and may hear and yet not understand.
John 12:37
But though He had performed such great miracles in their presence, they did not believe in Him--
Acts 28:25
Unable to agree among themselves, they at last left him, but not before Paul had spoken a parting word to them, saying, "Right well did the Holy Spirit say to your forefathers through the Prophet Isaiah:
Romans 11:8
And so Scripture says, "God has given them a spirit of drowsiness--eyes to see nothing with and ears to hear nothing with--even until now."

Be converted

Acts 3:19
Repent, therefore, and reform your lives, so that the record of your sins may be cancelled, and that there may come seasons of revival from the Lord,
2 Timothy 2:25
He must speak in a gentle tone when correcting the errors of opponents, in the hope that God will at last give them repentance, for them to come to a full knowledge of the truth
Hebrews 6:6
it is impossible, I say, to keep bringing them back to a new repentance, for, to their own undoing, they are repeatedly crucifying the Son of God afresh and exposing Him to open shame.