Delusion is defined as:

De·lu·sion /dəˈlo͞oZHən/ noun: delusion; plural noun: delusions

An idiosyncratic belief or impression that is firmly maintained despite being contradicted by what is generally accepted as reality or rational argument, typically a symptom of mental disorder.

“The delusion of being watched.”

“Was her belief in his fidelity just a delusion?”

The action of deluding someone or the state of being deluded.

“What a capacity television has for delusion.”

And, perhaps more directly:

De·lude /dəˈlo͞od/ verb: delude; 3rd person present: deludes; past tense and past participle: deluded; gerund or present participle: deluding

Impose a misleading belief upon (someone); deceive; fool.

“Too many theorists have deluded the public.”

In the second letter to the Thessalonians, the Apostle Paul speaks of deluding influences and the man of lawlessness:

Now concerning the coming of our Lord Jesus Christ and our being gathered together to him, we ask you, brothers, not to be quickly shaken in mind or alarmed, either by a spirit or a spoken word, or a letter seeming to be from us, to the effect that the day of the Lord has come.

Let no one deceive you in any way. For that day will not come, unless the rebellion comes first, and the man of lawlessness is revealed, the son of destruction, who opposes and exalts himself against every so-called god or object of worship, so that he takes his seat in the temple of God, proclaiming himself to be God.

Do you not remember that when I was still with you I told you these things? And you know what is restraining him now so that he may be revealed in his time. For the mystery of lawlessness is already at work. Only he who now restrains it will do so until he is out of the way. And then the lawless one will be revealed, whom the Lord Jesus will kill with the breath of his mouth and bring to nothing by the appearance of his coming.

The coming of the lawless one is by the activity of Satan with all power and false signs and wonders, and with all wicked deception for those who are perishing, because they refused to love the truth and so be saved. Therefore God sends them a strong delusion, so that they may believe what is false, in order that all may be condemned who did not believe the truth but had pleasure in unrighteousness [emphasis added].

2 Thessalonians 2:1-12 English Standard Version (ESV)

Calvin has much to say about these verses: 1–2, 3–4, 5–8, and 9–12. We’ll concentrate on what he said about verses 11 and 12:

Verse 11 – The working of delusion. He means that errors will not merely have a place, but [that] the wicked will be blinded, so…they will rush forward to ruin without consideration.

For as God enlightens us inwardly by his Spirit, that his doctrine may be efficacious in us, and opens our eyes and hearts, that it may make its way thither, so by a righteous judgment he delivers over to a reprobate mind (Romans 1:28) those whom he has appointed to destruction, that with closed eyes and a senseless mind, they may, as if bewitched, deliver themselves over to Satan and his ministers to be deceived…

Verse 12 – That all may be condemned. That is, that they may receive the punishment due to their impiety. Thus, those that perish have no just ground to expostulate with God, inasmuch as they have obtained what they sought.

For we must keep in view what is stated in Deuteronomy 13:3, that the hearts of men are subjected to trial, when false doctrines come abroad, inasmuch as they [the false doctrines] have no power except among those who do not love God with a sincere heart. Let those, then, who take pleasure in unrighteousness, reap the fruit of it.

When he says all, he means that contempt of God finds no excuse in the great crowd and multitude of those who refuse to obey the gospel, for God is the Judge of the whole world, so that he will inflict punishment upon a hundred thousand, no less than upon one individual.

The participle εὐδοκήσαντες (taking pleasure) means (so to speak) a voluntary inclination to evil, for in this way every excuse is cut off from the ungrateful, when they take so much pleasure in unrighteousness, as to prefer it to the righteousness of God.

For by what violence will they say that they have been impelled to alienate themselves by a mad revolt from God, towards whom they were led by the guidance of nature? It is at least manifest that they willingly and knowingly lent an ear to falsehoods.

But none of this is new. Throughout history and in all lands, God has given over the disobedient.

Roughly seven hundred years before Christ and more than a century and a half before their decreed release by Cyrus the Great, the prophet Isaiah encouraged the future Babylonian exiles to flee from there and, by faith, return to the Promised Land. Speaking of their spiritual blindness, he says to them:

They know not, nor do they discern, for he has shut their eyes, so that they cannot see, and their hearts, so that they cannot understand. Isaiah 44:18 (ESV)

Speaking to His disciples about the crowds gathered by the Sea of Galilee to hear Him, the Lord Jesus Christ cites Isaiah (Is. 6:9–10):

And he said to them, “To you has been given the secret of the kingdom of God, but for those outside everything is in parables, so that

“they may indeed see but not perceive,

    and may indeed hear but not understand,

lest they should turn and be forgiven.”

Mark 4:11-12 (ESV)

Later, during Lord’s entry into Jerusalem prior to the Passover, John recounts what Isaiah said about God’s hardening of hearts as a commentary on those who did not believe in the Lord:

“He has blinded their eyes

    and hardened their heart,

lest they see with their eyes,

    and understand with their heart, and turn,

    and I would heal them.”

John 12:40 (ESV)

Later still, Paul, in his letter to the church in Rome says:

So then he has mercy on whomever he wills, and he hardens whomever he wills. Romans 9:18 (ESV)

This is a clear expression of God’s sovereign kindness and severity.

And yet, He sets Eternity in the heart:

He has made everything beautiful in its time. Also, he has put eternity into man’s heart, yet so that he cannot find out what God has done from the beginning to the end. Ecclesiastes 3:11 (ESV)

Truly, His ways are past finding out:

Oh, the depth of the riches and wisdom and knowledge of God! How unsearchable are his judgments and how inscrutable his ways! Romans 11:33 (ESV)

Even though we deserve ruthlessness, He Himself seeks to persuade us with rational arguments:

“Come now, let us reason together, says the Lord:

Though your sins are like scarlet, they shall be as white as snow;

Though they are red like crimson, they shall become like wool.

If you are willing and obedient, you shall eat the good of the land;

But if you refuse and rebel,you shall be eaten by the sword;

For the mouth of the Lord has spoken.”

Isaiah 1:18–20 (ESV)

Then, of course, He speaks to us of an unmerited gift:

Come to me, all who labor and are heavy laden, and I will give you rest. Take my yoke upon you, and learn from me, for I am gentle and lowly in heart, and you will find rest for your souls. Matthew 11:28-29 (ESV)

With Paul (and Isaiah), I say to you: sleeper, awake!