You left out much of the passage.
2 Cor 4:3 But if our gospel be hid, it is hid to them that are lost:
4 In whom the god of this world hath blinded the minds of them which believe not, lest the light of the glorious gospel of Christ, who is the image of God, should shine unto them.
5 For we preach not ourselves, but Christ Jesus the Lord; and ourselves your servants for Jesus' sake.
6 For God, who commanded the light to shine out of darkness, hath shined in our hearts, to give the light of the knowledge of the glory of God in the face of Jesus Christ.
Verse 4 shows that Satan hath blinded the minds of them which believe not.
Now, I don't know if I can make you understand, but God gives every man what he wants, even the unsaved. Because they do not want to know God, because they do not want to understand the truth, God gives them exactly that. He allows Satan to deceive and blind them. But it is because they loved sin to begin with.
An example of this is king Ahab in 1 Kings. Ahab wanted to go to war against the king of Syria. He called Jehoshaphat king of Judah to join him.
1 Kings 22:4 And he said unto Jehoshaphat, Wilt thou go with me to battle to Ramothgilead? And Jehoshaphat said to the king of Israel, I am as thou art, my people as thy people, my horses as thy horses.
Jehoshaphat wanted to enquire of the prophets before undertaking this battle.
1 Kings 22:5 And Jehoshaphat said unto the king of Israel, Inquire, I pray thee, at the word of the LORD to day.
Ahab brought 400 prophets who all prophesied that Ahab would be successful.
1 Kings 22:6 Then the king of Israel gathered the prophets together, about four hundred men, and said unto them, Shall I go against Ramothgilead to battle, or shall I forbear? And they said, Go up; for the Lord shall deliver it into the hand of the king.
Jehoshaphat apparently did not believe these prophets, for he asked if there could be found a prophet of the Lord.
1 Kings 22:7 And Jehoshaphat said, Is there not here a prophet of the LORD besides, that we might inquire of him?
Ahab answered yes, there was one named Micaiah, but he hated this prophet, because he always prophesied against him.
1 Kings 22:8 And the king of Israel said unto Jehoshaphat, There is yet one man, Micaiah the son of Imlah, by whom we may inquire of the LORD: but I hate him; for he doth not prophesy good concerning me, but evil. And Jehoshaphat said, Let not the king say so.
9 Then the king of Israel called an officer, and said, Hasten hither Micaiah the son of Imlah.
In the meanwhile, the false prophets continued to prophesy success.
1 Kings 22:10 And the king of Israel and Jehoshaphat the king of Judah sat each on his throne, having put on their robes, in a void place in the entrance of the gate of Samaria; and all the prophets prophesied before them.
11 And Zedekiah the son of Chenaanah made him horns of iron: and he said, Thus saith the LORD, With these shalt thou push the Syrians, until thou have consumed them.
12 And all the prophets prophesied so, saying, Go up to Ramothgilead, and prosper: for the LORD shall deliver it into the king's hand.
The messenger who went to call Micaiah tried to convince him to give the same prophesy as the false prophets. Micaiah said he would only say what the Lord told him.
1 Kings 22:13 And the messenger that was gone to call Micaiah spake unto him, saying, Behold now, the words of the prophets declare good unto the king with one mouth: let thy word, I pray thee, be like the word of one of them, and speak that which is good.
14 And Micaiah said, As the LORD liveth, what the LORD saith unto me, that will I speak.
Now here is where it gets real interesting. Micaiah also prophesied that Ahab would be successful. And Ahab did not believe him!
1 Kings 22:15 So he came to the king. And the king said unto him, Micaiah, shall we go against Ramothgilead to battle, or shall we forbear? And he answered him, Go, and prosper: for the LORD shall deliver it into the hand of the king.
16 And the king said unto him, How many times shall I adjure thee that thou tell me nothing but that which is true in the name of the LORD?
I think deep in his heart Ahab knew his 400 prophets were false, chosen simply because they told Ahab what he wanted to hear, not the truth. So, he did not believe when Micaiah agreed with the false prophets and asked for the truth. Now Micaiah reveals that God had sent a lying spirit to lie through Ahab's false prophets.
1 Kings 22:17 And he said, I saw all Israel scattered upon the hills, as sheep that have not a shepherd: and the LORD said, These have no master: let them return every man to his house in peace.
18 And the king of Israel said unto Jehoshaphat, Did I not tell thee that he would prophesy no good concerning me, but evil?
19 And he said, Hear thou therefore the word of the LORD: I saw the LORD sitting on his throne, and all the host of heaven standing by him on his right hand and on his left.
20 And the LORD said, Who shall persuade Ahab, that he may go up and fall at Ramothgilead? And one said on this manner, and another said on that manner.
21 And there came forth a spirit, and stood before the LORD, and said, I will persuade him.
22 And the LORD said unto him, Wherewith? And he said, I will go forth, and I will be a lying spirit in the mouth of all his prophets. And he said, Thou shalt persuade him, and prevail also: go forth, and do so.
23 Now therefore, behold, the LORD hath put a lying spirit in the mouth of all these thy prophets, and the LORD hath spoken evil concerning thee.
Because Ahab was not sincerely interested in God's word and hated God's true prophet Micaiah, God sent a lying spirit to Ahab's false prophets to tell Ahab what he wanted to hear. When Micaiah told the truth, Ahab had Micaiah imprisoned.
1 Kings 22:24 But Zedekiah the son of Chenaanah went near, and smote Micaiah on the cheek, and said, Which way went the Spirit of the LORD from me to speak unto thee?
25 And Micaiah said, Behold, thou shalt see in that day, when thou shalt go into an inner chamber to hide thyself.
26 And the king of Israel said, Take Micaiah, and carry him back unto Amon the governor of the city, and to Joash the king's son;
27 And say, Thus saith the king, Put this fellow in the prison, and feed him with bread of affliction and with water of affliction, until I come in peace.
Ahab said to imprison Micaiah until he returned in peace. But Micaiah said that if Ahab returned, then the Lord had not spoken by him.
1 Kings 22:28 And Micaiah said, If thou return at all in peace, the LORD hath not spoken by me. And he said, Hearken, O people, every one of you.
29 So the king of Israel and Jehoshaphat the king of Judah went up to Ramothgilead.
30 And the king of Israel said unto Jehoshaphat, I will disguise myself, and enter into the battle; but put thou on thy robes. And the king of Israel disguised himself, and went into the battle.
31 But the king of Syria commanded his thirty and two captains that had rule over his chariots, saying, Fight neither with small nor great, save only with the king of Israel.
32 And it came to pass, when the captains of the chariots saw Jehoshaphat, that they said, Surely it is the king of Israel. And they turned aside to fight against him: and Jehoshaphat cried out.
33 And it came to pass, when the captains of the chariots perceived that it was not the king of Israel, that they turned back from pursuing him. 34 And a certain man drew a bow at a venture, and smote the king of Israel between the joints of the harness: wherefore he said unto the driver of his chariot, Turn thine hand, and carry me out of the host; for I am wounded.
35 And the battle increased that day: and the king was stayed up in his chariot against the Syrians, and died at even: and the blood ran out of the wound into the midst of the chariot.
So, you can see that Ahab ignored Micaiah when Micaiah told him the truth. Ahab preferred to believe a lie, so God allowed a lying spirit to prophesy by his false prophets that he would succeed. And so Ahab was killed in battle.
God does not cause a man to sin. But because men do not love the truth and love sin, God will allow them to be deceived.
2 Thess 2:8 And then shall that Wicked be revealed, whom the Lord shall consume with the spirit of his mouth, and shall destroy with the brightness of his coming:
9 Even him, whose coming is after the working of Satan with all power and signs and lying wonders,
10 And with all deceivableness of unrighteousness in them that perish; because they received not the love of the truth, that they might be saved.
11 And for this cause God shall send them strong delusion, that they should believe a lie:
12 That they all might be damned who believed not the truth, but had pleasure in unrighteousness.