Now, some would debate that the departure is called the falling away in many translations and it means an apostasy or departure from Christianity, but that is taking a lot of liberty with the text. Every major translation prior to the KJV translated the passage as simply "departure" or "the departure". Even the Latin Vulgate from the 4th century uses discessio which means a physical, spatial departure, not a spiritual one.
"Apostasia" as "rapture" was unknown in Christian orthodoxy until its sudden appearance in 1895.
Here is the elaboration on 2 Thes. 2:3 in the Wycliffe translation:
3 [That] No man deceive you in any manner. For but dissension come first [For no but departing away, or dissension, shall come first], and the man of sin be showed, the son of perdition
Note that dissension (consistent with apostasy, separation, schism) is the elaboration. Rapture is unseen.
Departing away as a synonym of dissension thus means departing away from the faith, i.e. apostasy, not rapture; falling away, not flying away.
Wycliffe identified the man of sin as the apostate papal antichrist, at whose hands the true church was suffering. He did not believe in a pretrib rapture of which he had never heard, and which had never occurred.
From Calvin's Geneva Study Bible:
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;
Calvin also identified the man of sin as the papacy, and did not believe in a pretrib rapture of which he had never heard, and which had never occurred.
Same with Tyndale. He was martyred by the papacy.
Same with Cranmer. He too was martyred by the papacy.
Coverdale was an associate of Tyndale's, and of like persuasion.
Beza was also of like persuasion.
There is
no Reformer who considered the word to mean anything other than
departure from the faith.
A definition of "discessio," the word used in the Vulgate, is found at
this site.
Included near the end is a specific ecclesiological subdefinition:
"In the church,
a separation, schism (eccl. Lat.),
Vulg. Act. 21, 21;
id. 2 Thes. 2, 3."
Occurrences are cited as being
Acts 21:21 and 2 Thes. 2:3.
Letting Scripture interpret Scripture, the use of the word in
Acts 21:21 is translated "forsake," which is fully consistent with the subdefinition above, and has nothing to do with rapture.
Apostacia: What Modern Greeks say about "Apostacia" in 2 Thess 2:3.
Excerpt: "I could find no debate among Greek speaking Christians on how to interpret this verse. They all interpret "apostacia" in 2 Thess 2:3 to mean "apostacy"."
Does Apostasia in 2 Thessalonians 2:3 Refer to a ‘Physical Departure’ (i.e. the Rapture)?
2 Thess 2:3 in the Early Church Writings; How early Greek, Latin and Aramaic speaking Christians interpreted "Apostacia"/"Apostacy
The Latin Influence on 2 Thess 2:3
Of the approximately fifty contemporary English Bible versions in existence,
not a single version translates "apostasia" as "rapture", but rather as
apostasy, falling away, or the equivalent.