Ephesians 4:18

they are darkened in their understanding, alienated from the life of God because of the ignorance that is in them, due to the hardness of their heart;

Ephesians 2:12

remember that you were at that time separate from Christ, excluded from the commonwealth of Israel, and strangers to the covenants of promise, having no hope and without God in the world.

Galatians 4:8

Formerly, when you did not know God, you were slaves to those which by nature are no gods.

1 Thessalonians 4:5

not in the passion of lust like the heathen, who do not know God;

Acts 17:30

The times of ignorance God overlooked, but now he commands all people everywhere to repent,

Romans 1:21-23

for although they knew God they did not honor him as God or give thanks to him, but they became futile in their thinking, and their foolish hearts were darkened.

Romans 11:25

I do not want you to be ignorant of this mystery, brothers, so that you may not be conceited: Israel has experienced a hardening in part until the full number of the Gentiles has come in.

Matthew 13:15

For this people's heart has grown dull. And their ears are hard of hearing, and their eyes they have closed, lest they should see with their eyes, and hear with their ears, and they understand with their hearts, and turn so that I should heal them.'

Mark 3:5

And he looked around at them with anger, grieved at the hardness of their hearts, and said to the man, "Stretch out your hand." He stretched it out, and his hand was restored.

John 12:40

"He has blinded their eyes and hardened their hearts, lest they should see with their eyes, and understand with their hearts and turn, so that I should heal them."

Acts 26:17-18

rescuing you from the Jewish people and from the Gentiles, to whom I am sending you,

Romans 1:28

And since they did not see fit to retain the knowledge of God, God gave them over to a base mind, to do what ought not to be done.

Romans 2:19

and if you are sure that you are a guide to the blind, a light to those who are in darkness,

Romans 8:7-8

For the mind that is set on the flesh is hostile to God; it does not submit to God's law, nor can it do so;

1 Corinthians 1:21

For since in the wisdom of God the world through its wisdom did not know God, God was pleased through the foolishness of what was preached to save those who believe.

2 Corinthians 3:14

But their minds were hardened; for to this day, when they read the old covenant, the same veil remains unlifted, because only in Christ is it removed.

2 Corinthians 4:4

In their case the god of this world has blinded the minds of the unbelievers, so that they might not see the light of the gospel of the glory of Christ, who is the image of God.

Colossians 1:21

And although you were once alienated and hostile in mind, doing evil deeds,

James 4:4

You adulteresses, do you not know that friendship with the world is hostility toward God? Therefore whoever wishes to be a friend of the world makes himself an enemy of God.

1 John 2:11

But he who hates his brother is in the darkness and walks in the darkness, and does not know where he is going, because the darkness has blinded his eyes.

Treasury of Scripture Knowledge

Summary

Having the understanding darkened, being alienated from the life of God through the ignorance that is in them, because of the blindness of their heart:

Bible References

The understanding

Acts 17:30
The times of ignorance God overlooked, but now he commands all people everywhere to repent,
Acts 26:17
rescuing you from the Jewish people and from the Gentiles, to whom I am sending you,
Romans 1:21
for although they knew God they did not honor him as God or give thanks to him, but they became futile in their thinking, and their foolish hearts were darkened.
1 Corinthians 1:21
For since in the wisdom of God the world through its wisdom did not know God, God was pleased through the foolishness of what was preached to save those who believe.
2 Corinthians 4:4
In their case the god of this world has blinded the minds of the unbelievers, so that they might not see the light of the gospel of the glory of Christ, who is the image of God.
Galatians 4:8
Formerly, when you did not know God, you were slaves to those which by nature are no gods.
1 Thessalonians 4:5
not in the passion of lust like the heathen, who do not know God;

Alienated

Ephesians 2:12
remember that you were at that time separate from Christ, excluded from the commonwealth of Israel, and strangers to the covenants of promise, having no hope and without God in the world.
Romans 8:7
For the mind that is set on the flesh is hostile to God; it does not submit to God's law, nor can it do so;
Galatians 4:8
Formerly, when you did not know God, you were slaves to those which by nature are no gods.
Colossians 1:21
And although you were once alienated and hostile in mind, doing evil deeds,
1 Thessalonians 4:5
not in the passion of lust like the heathen, who do not know God;
James 4:4
You adulteresses, do you not know that friendship with the world is hostility toward God? Therefore whoever wishes to be a friend of the world makes himself an enemy of God.

Because

Romans 1:21
for although they knew God they did not honor him as God or give thanks to him, but they became futile in their thinking, and their foolish hearts were darkened.
Romans 2:19
and if you are sure that you are a guide to the blind, a light to those who are in darkness,
1 John 2:11
But he who hates his brother is in the darkness and walks in the darkness, and does not know where he is going, because the darkness has blinded his eyes.