I hardly know where to begin. It seems like you've done enough total Bible study, so I'm a bit surprised you're not aware of what the "strong delusion" of 2 Thess.2 is.
Remember in 2 Thess.2, Apostle Paul said two events must happen first, prior to Christ's coming and our gathering to Him. There must first be a great apostasy (falling away), and the man of sin must be revealed sitting in a temple in Jerusalem (early 1st century Church father interpretation). Paul showed how that false one will work great signs and wonders, and exalt himself as God, and over all that is called God, or that is worshiped.
In Matthew 24, our Lord Jesus showed seven main signs of the very end of this world. Early in the chapter He warned of many coming in His name saying they are Christ. But... in the Matt.24:23-26 verses, He was pointing to a singular false messiah coming to deceive, working the great signs and wonders that if possible, would deceive even His very elect. In that, He linked it to the time of the end of this world with the "great tribulation" He mentioned.
Likewise in 1 John 2:18, John was pointing to a singular coming antichrist figure, and the idea of many antichrists. John said they had heard that antichrist would come, and that's about the singular antichrist Jesus warned about in those Matt.24:23-26 verses. In Matthew 24:24, the KJV translators brought the Greek word pseudochristos into English as "false Christs" plural. But the actual Greek word is made up of two Greek words, pseudo which means false or fake, and Christos which means Christ, singular. When the deceived come up to us and say, "Lo, here is Christ, or there", that's about a singular false Christ, not many. So this difference must be understood because our Lord Jesus covered both the coming singular antichrist, and the many antichrists, just as Apostle Paul also did in 2 Thess.2.
In 2 Thess.2, Paul was covering the idea of a coming singular antichrist ("man of sin") and the many antichrists ("mystery of iniquity"). The 'mystery of iniquity' idea is from the Old Testament about the "workers of iniquity". It relates to Christ's parable of the tares of the field. If you don't understand the tares parable, you probably won't understand that "mystery of iniquity". But essentially, it's really just about the many antichrists that follow the devil, i.e., the children of darkness, the workers of iniquity.
2 Thess.2 reveals the coming of the pseudo-Christ of Matt.24:23-26. It is the same "another beast" of Rev.13 that is to work those great signs and miracles, making fire come down from heaven in the sight of men. He will institute an idol in false worship for all to bow to, much in the same way the king of Babylon did during Daniel's days. He will claim to be The Christ, which is what his having two horns like a lamb points to.
The word antichrist really is not specific enough for what the coming false one is to do on earth at the very end per those Scriptures. Greek pseudo-Christ, or false-Messiah is more fitting. So who would believe that coming pseudo-Christ could be the True Christ Jesus, the True Messiah? It should be easy to understand how the orthodox Jews will believe it. It should also be easy to understand how deceived brethren in Christ's Church might 'fall away' to that fake, and become apostates, and no longer found as a "chaste virgin" to Jesus when He does return afterwards.
Where did this sin of a false one wanting to be God originate?
It was the very first sin, the sin of what Satan did in the time of old at his original rebellion against God. It was his job to guard God's Throne and he instead coveted God's Throne for himself, wanting to be God. That is exactly what the coming false one of 2 Thess.2 is trying to do in Jerusalem, i.e., set himself up in place of God to be worshiped as God.
That... is what the "strong delusion" of that 2 Thess.2 chapter is about. Those who fall away to that false one in thinking he is our Lord Jesus having returned, or the orthodox Jews thinking that is Messiah, or any of the other religions on earth beliving that is their awaited holy one, that all represents falling away to the "strong delusion" God has setup for the deceived in the end.
I get what you are saying. It is the same as I have been instructed for most of my life. Endtimes: This happens, and then this, and then this...in a neat plan. For me, enough questions have been raised for me to realize I
should ask questions:
One) What is the temple of God? We are told our sight and affection is to be above; on THAT Jerusalem which is above, which Jerusalem we are citizens of.
Revelation 21:22-27
[22] And I saw no temple therein: for the Lord God Almighty and the Lamb are the temple of it. [23] And the city had no need of the sun, neither of the moon, to shine in it: for the glory of God did lighten it, and the Lamb is the light thereof. [24] And the nations of them which are saved shall walk in the light of it: and the kings of the earth do bring their glory and honour into it. [25] And the gates of it shall not be shut at all by day: for there shall be no night there. [26] And they shall bring the glory and honour of the nations into it. [27]
And there shall in no wise enter into it any thing that defileth, neither whatsoever worketh abomination, or maketh a lie: but they which are written in the Lamb's book of life.
So how is he (singular) going to defile it?
In Luke 13:27-29 who is being spoken to: [27] But he shall say, I tell you, I know you not whence ye are; depart from me, all ye workers of iniquity. [28] There shall be weeping and gnashing of teeth, when ye shall see Abraham, and Isaac, and Jacob, and all the prophets, in the kingdom of God, and you yourselves thrust out. [29] And they shall come from the east, and from the west, and from the north, and from the south, and shall sit down in the kingdom of God.
There are many false prophets and antichrist. yes, they are controlled by the head which is anti...:same as we are led by our head which IS Christ.
Judas was called the son of perdition. (So that the scripture is fulfilled.)
Revelation 17:16-17
[16] And the ten horns which thou sawest upon the beast, these shall hate the whore, and shall make her desolate and naked, and shall eat her flesh, and burn her with fire. [17] For God hath put in their hearts to fulfil his will, and to agree, and give their kingdom unto the beast,
until the words of God shall be fulfilled. --we see this image in Daniel. Kingdoms through out history that give their power to the beast (all lead by one head:antichrist) until that final Kingdom breaks and consumes all the others.
Settle for me why God would destroy a temple made-with-hands and build a spiritual house of God...only to go back to the OT of flesh for a seven year period where a man stands in a man-made temple and claims he is God?
Anti-Christ has been going on:
Acts 19:26-29
[26] Moreover ye see and hear, that not alone at Ephesus, but almost throughout all Asia, this Paul hath persuaded and turned away much people, saying that they be no gods, which are made with hands: [27] So that not only this our craft is in danger to be set at nought; but also that the temple of the great goddess Diana should be despised, and her magnificence should be destroyed, whom all Asia and the world worshippeth. [28] And when they heard these sayings ,
they were full of wrath, and cried out, saying, Great is Diana of the Ephesians. [29] And the whole city was filled with confusion: and having caught Gaius and Aristarchus, men of Macedonia, Paul's companions in travel, they rushed with one accord into the theatre.
Confusion. Which brings a final point. The delusion is: who do you say Jesus Christ is?
John 12:34-43
[34] The people answered him, We have heard out of the law that Christ abideth for ever: and how sayest thou, The Son of man must be lifted up?
who is this Son of man? [35] Then Jesus said unto them, Yet a little while is the light with you. Walk while ye have the light, lest darkness come upon you: for he that walketh in darkness knoweth not whither he goeth. [36] While ye have light, believe in the light, that ye may be the children of light. These things spake Jesus, and departed, and did hide himself from them. [37] But though he had done so many miracles before them, yet they believed not on him: [38] That the saying of Esaias the prophet might be fulfilled, which he spake, Lord, who hath believed our report? and to whom hath the arm of the Lord been revealed? [39] Therefore they could not believe, because that Esaias said again, [40] He hath
blinded their eyes, and hardened their heart; that they should not see with their eyes, nor understand with their heart, and be converted, and I should heal them. [41] These things said Esaias, when he saw his glory, and spake of him. [42] Nevertheless among the chief rulers also many believed on him; but because of the Pharisees they did not confess him , lest they should be put out of the synagogue: [43] For they loved the praise of men more than the praise of God.
Notice God choose of those that had not bowed a knee to other idols and blinded the rest. Two distinct groups. The elect. And those blinded. The elect see Christ. Those blind do not see Christ. We are not waiting for the elect to open their eyes, because He never blinded them. It was "the rest" God blinded.
Romans 11:4
[4] But what saith the answer of God unto him? I have reserved to myself seven thousand men, who have not bowed the knee to the image of Baal.