For those who believe in a pre-trib rapture, the most common passage to use in defense of that position is 1st Thessalonians 4:15>17, and that the first few verses in 2nd Thessalonians are talking about the man of sin/tribulation.
Well, actually 2nd Thessalonians 2:3 shows the rapture before the man of sin is revealed.
"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"
The words "Falling away" have been used for over 400 years to describe somehow that people lose their faith, or they stop believing, or they give-up faith/believe.
Those words "Falling away" only started in 1611 with the KJV.
The original Greek text uses, "n apostaooia", (sorry, I can't type the accent marks,) and the original meaning did not mean what we call "Apostate", as in "become an apostate", or "fall away from faith".
The original meaning of "apostaooia" was "Departing", the little "n" prefix signified A ONE TIME EVENT.
People have been "falling away" from the faith since Adam, that's been ongoing since then, where "n apostaooia" is a singular event.
1, 382AD Jerome's Latin Vulgate, "Departure first".
2, 1384 Wycliff Bible, "Departynge first".
3, 1526 Tyndale Bible, "Departynge first".
4, 1535 Cloverdale Bible, "Departynge first".
5, 1539 Crammer Bible, "Departing first".
6, 1576 Breeches Bible, "Departing first".
7, 1583 Beeza Bible, "Departing first".
8, 1608 Geneva Bible, "Departing first".
9, 1611 King James Bible, "Falling away".
The word "Harpazo" is a "snatching away", the difference between Harpazo and "n apostaoosia" is a matter of degree not one of different action, the two might be considered as "will vs shall", they both imply the same outcome.
One might also notice that Paul didn't say anything about "departing from the faith", to use the original language, what he said was: ",,,,,that day shall not come, unless there come a departure first".
The "departure" is the church "departing first" before the man of sin is revealed.
How did it get changed in the KJV? I have no idea, perhaps one of the scribes had an extra glass of wine at lunchtime.