“And Jesus answered and said unto them, Take heed that no man deceive you.” (Mt. 24:4)
From The Christian Church in the Last Days
If the Christian church is not raptured pretribulation and is on the earth for some of Daniel’s seven-year tribulation, a more plausible motivation for nominal churchgoers to fall away would be the hard choice of facing persecution along with the genuine church, compared to the easier choice of saving their own skins by compromising with the direction the world is going in accepting the mark of the beast. Or some application of Daniel 8:23-25 might explain large numbers of nominal churchgoers mistakenly falling away to follow the deceptive and smooth-talking appeal of the Antichrist at the beginning of his reign of falsely promised peace and worldly prosperity. This might presumably be followed up with a more complete falling away after persecution begins for the genuine Christians (saints of the Most High) who are not taken-in by the deceptive appeal of the Antichrist (Revelation 13:16-17).
Because of the unique character of post-rapture tribulation saints, the falling away that Paul describes in 2 Thessalonians 2:2-3 would not likely occur between the time period of a pretribulation rapture of the church and the second coming of Christ seven years later. In a pretribulation rapture scenario, the tribulation saints that become Christian believers after the rapture are probably a hard-core, uncompromising group of determined disciples, having themselves missed the rapture, who will not fall away in large numbers as a result of anything that comes against them during the tribulation period. All of the “left behind” nominal churchgoers who do not become tribulation saints would quickly be absorbed into the world-at-large and quietly fade away into the background. The characteristically hard-core, resolute commitment of last-days tribulation saints, steeled in their faith by the knowledge that their conversion came too late to participate in the rapture, eliminates them as plausible candidates to fall away under harsh persecution.
Continuing this argument, once the church is raptured (pretribulation) and gone, the contrasting spiritual makeup of the remaining cast of characters would be rigidly polarized and separated for the rest of the tribulation period. Remove hundreds of millions of Spirit-born Christians from the earth, and the current reality of a large, undecided, unbelieving composite mix of people co-existing undetected within churches would overnight become a separate and homogenous group, totally distinct from the soon-to-be converted, immerging group of tribulation saints. From that time forward, post-rapture, there would be no internal motivation based on shared common beliefs, nor the existence of external communication channels recently in place in organized Christian church structures, for these two dissimilar groups to merge. The zeal and determined dedication of the tribulation saints to become and to remain faithful Christians “come what may,” would separate out tribulation saints as a uniquely zealous and distinct group of people for the remainder of the tribulation period.
Paul presents the falling away and the revelation of the son of perdition as signs leading up to the rapture. The rapture and the falling away cannot be bundled together in reverse order within a short time-span. The magnitude of the rapture would completely overshadow any subsequent falling away.