Ephesians 4:18

being darkened in their understanding, alienated from the life of God through the ignorance being in themselves, on account of the blindness of their heart;

Ephesians 2:12

because you were at that time without Christ, being alienated from the commonwealth of Israel, and strangers of the covenants of the promise, having no hope and being atheists in the world.

1 Thessalonians 4:5

not in the passion of lust, as indeed the Gentiles who do not know God;

Acts 17:30

Then indeed God winking at the times of ignorance, now commands all men everywhere to repent:

Romans 1:21-23

because, knowing God, they did not glorify Him as God, neither were they thankful; but they became vain in their reasonings, and their foolish heart was darkened.

Romans 11:25

I do not wish you to be ignorant, brethren, as to this mystery, in order that you may not he wise with yourselves, that blindness in part has happened unto Israel, until the fulness of the Gentiles may come in;

Matthew 13:15

Because the heart of this people is waxed gross, and they heard heavily with their ears, and closed their eyes; lest they may see with their eyes, and hear with their ears, and understand with their hearts, and turn, and I shall heal them.

Mark 3:5

And looking round on them with indignation, being grieved over the hardness of their hearts, He says to the man; Reach forth thy hand. And he reached it forth and it was restored.

John 12:40

He hath blinded their eyes, and hardened their heart; in order that they may not see with their eyes, nor understand with their heart, and turn, and I shall heal them.

Acts 26:17-18

delivering thee from the people, and from the Gentiles, unto whom now I send thee,

Romans 1:28

And as they did not approve to have God in their knowledge, God gave them up to a reprobate mind, to do those things which are inappropriate;

Romans 2:19

and persuade yourself that you are a guide of the blind, a light of those who are in darkness, an instructor of the ignorant,

Romans 8:7-8

Therefore the mind of depravity is enmity toward God: for it is not subordinated to the law of God, for it is not able so to be.

1 Corinthians 1:21

For since in the wisdom of God the world by wisdom knew not God, God was pleased through the foolishness of preaching to save those who believe.

2 Corinthians 3:14

But their minds were darkened. For until this day the same veil remains in the reading of the old covenant, remains, not lifted; because it is done away in Christ;

2 Corinthians 4:4

in whom the god of this age has blinded the minds of those who believe not, in order that the light of the gospel of the glory of Christ, who is the image of God, may not shine on them.

Colossians 1:21

And you, being at one time aliens and enemies in your minds on account of wicked works, nevertheless he has now reconciled

James 4:4

O adulteresses, do you not know that the friendship of the world is enmity to God? Whosoever therefore may wish to be the friend of the world renders himself the enemy of God.

1 John 2:11

But the one hating his brother is in darkness, and walks about in darkness, and does not know whither 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
Then indeed God winking at the times of ignorance, now commands all men everywhere to repent:
Acts 26:17
delivering thee from the people, and from the Gentiles, unto whom now I send thee,
Romans 1:21
because, knowing God, they did not glorify Him as God, neither were they thankful; but they became vain in their reasonings, and their foolish heart was darkened.
1 Corinthians 1:21
For since in the wisdom of God the world by wisdom knew not God, God was pleased through the foolishness of preaching to save those who believe.
2 Corinthians 4:4
in whom the god of this age has blinded the minds of those who believe not, in order that the light of the gospel of the glory of Christ, who is the image of God, may not shine on them.
1 Thessalonians 4:5
not in the passion of lust, as indeed the Gentiles who do not know God;

Alienated

Ephesians 2:12
because you were at that time without Christ, being alienated from the commonwealth of Israel, and strangers of the covenants of the promise, having no hope and being atheists in the world.
Romans 8:7
Therefore the mind of depravity is enmity toward God: for it is not subordinated to the law of God, for it is not able so to be.
Colossians 1:21
And you, being at one time aliens and enemies in your minds on account of wicked works, nevertheless he has now reconciled
1 Thessalonians 4:5
not in the passion of lust, as indeed the Gentiles who do not know God;
James 4:4
O adulteresses, do you not know that the friendship of the world is enmity to God? Whosoever therefore may wish to be the friend of the world renders himself the enemy of God.

Because

Romans 1:21
because, knowing God, they did not glorify Him as God, neither were they thankful; but they became vain in their reasonings, and their foolish heart was darkened.
Romans 2:19
and persuade yourself that you are a guide of the blind, a light of those who are in darkness, an instructor of the ignorant,
1 John 2:11
But the one hating his brother is in darkness, and walks about in darkness, and does not know whither he is going, because the darkness has blinded his eyes.