The Thessalonian believers in Paul’s second epistle were suffering because of persecution. They made the mistake of thinking that they were experiencing the day of the Lord’s wrath because of this. Paul writes back and reassures them that the day of the Lord’s wrath has not come, because two events must happen first: the apostasy and the Antichrist’s revelation. Therefore, they do not have to be quickly shaken in mind or alarmed.
Sadly, and ironically, pretribulational believers today commit the exact same error because they have been taught that the Antichrist’s great tribulation is the same event as the day of the Lord’ wrath. In other words, they are confusing eschatological persecution with God’s future judgment. Thus, just as the Thessalonians were quickly shaken in mind and alarmed, pretribbers will do likewise when the Antichrist arrives and begins to persecute them.