1 Now we beseech you, brethren, by the coming of our Lord Jesus Christ, and by our gathering together unto him, 2 That ye be not soon shaken in mind, or be troubled, neither by spirit, nor by word, nor by letter as from us, as that the day of Christ is at hand. 3 Let no man deceive you by any means: for that day shall not come, except there come a falling away first, and that man of sin be revealed, the son of perdition; 4 Who opposeth and exalteth himself above all that is called God, or that is worshipped; so that he as God sitteth in the temple of God, shewing himself that he is God. 5 Remember ye not, that, when I was yet with you, I told you these things? 6 And now ye know what withholdeth that he might be revealed in his time. 7 For the mystery of iniquity doth already work: only he who now letteth will let, until he be taken out of the way. 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.

2 Thessalonians 2
King James Bible

Paul refers to 2 events here in verse 1:

1. "by the coming of our Lord Jesus Christ"
2. "and by our gathering together unto him"

The first is the Day of the Lord(Christ) and the second is the rapture(gathering together)

We are then warned to "not soon shaken in mind, or be troubled, neither by spirit, nor by word, nor by letter as from us, as that the day of Christ is at hand"

They were worried they were living in the Day of the Lord. But Paul clearly shows them that that day CANNOT come until other things happen:

1. "except there come a falling away first"
2. "and that man of sin be revealed, the son of perdition"

The Day of the Lord is the tribulation period. But that day cannot come until 2 other events occur, the falling away and the revealing of the man of sin.

So what is the falling away? Paul reiterates it in verse 6:

"And now ye know what withholdeth that he might be revealed in his time. 7 For the mystery of iniquity doth already work: only he who now letteth will let, until he be taken out of the way. 8 And then shall that Wicked be revealed

So, here's the order. He(The Holy Spirit) who indwells all believers is preventing the revealing of the antichrist. He is the restrainer of evil. The "saltness" of the believers, who are the vessels(temple) of the Holy Spirit, is preventing the revealing of pure evil. Once the rapture occurs the restrainer of evil is "taken out of the way".

Rapture then revealing
falling away first, and that man of sin be revealed

These verses are parallel. The falling away is really the "catching away" of the Church. Or if you will, the falling away of the Holy Spirit from the earth. Once you see this it all becomes clear. The great falling away is not an apostasy, it is the departure of the Holy Spirit from the earth which precedes the revealing of the antichrist