The situation in Thessalonica has changed since Paul wrote his first letter to the church. In fact, the second letter is so different from the first that some scholars suggest it was actually the first letter Paul wrote to the church and the order was reversed as the early church gathered the Pauline letters into a collection. It is true the whole collection is not chronological, and the general order of the letters is from longest (Romans) to the shortest (Philemon). So it is possible the smaller 2 Thessalonians was placed after the first letter simply because it was shorter. In the absence of evidence, this reversal of the letters is too speculative, and it really does not take into account 1 Thessalonians fits well into the context of Acts.
As for the situation of the letter, the consensus view is that the church received a letter claiming to come from Paul has circulated to the church. This letter claimed the “Day of the Lord” has already occurred. Paul writes to calm their fears and to assure then that the Day of the Lord has not yet arrived since the “Man of Lawlessness” has not been revealed.
But there is more in the background than a false letter claiming the “end times” have begun. It is possible the persecution the church faced has caused some in the congregation to wonder if they are suffering because they have sinned (and are being punished) or perhaps have believed the wrong things about Jesus. Much of the Greco-Roman world was motivated by pursuit of honor and avoiding shame. The suffering the church is facing appears to be “shame” rather than an “honor.” Paul taught them Jesus would return soon and render judgment, yet he has not returned to rescue the Thessalonians from their troubles.
Why does Paul write 2 Thessalonians?
First, Paul writes this second letter to clarify that Christians might suffer before the return of the Lord. First, suffering cannot be taken as an indication that the Great Tribulation has begun because God has an appointed time when the restraining power of God is removed from the world, permitting the Lawless One to be revealed.
Second, suffering should not be taken as an indication of divine disfavor. Nor should the Christian think they are dishonored because they are being persecuted. This sort of suffering is the lot of the Christian and the endurance the church has already demonstrated is a worthy testimony of the Lord’s work in their church and is a source of boasting for Paul. Paul is pleased that they are steadfast as they endure persecution (1:4).
Third, the source of the suffering which the church is experiencing is not God, but rather Satan. God is not punishing them at all. Since they are a successful, growing church, Satan is attempting to distract them from their calling as a church. They are engaged in serious spiritual warfare, so they ought to “stand firm and hold fast to the teachings” Paul had already passed on to them (2:15).
Fourth, the central problem in 2 Thessalonians is the false report about the return of Christ (2:1-12). Paul first must remind the Thessalonians of what he has already taught them, that the Lord will not return until “the man of lawlessness” is revealed, and this person cannot be revealed until “the restraining force” is taken out of the way. The identity of the Restrainer is one of the more difficult issues in Pauline studies (here are a few comments on what Paul might be talking about). Setting aside the precise identity of the Restrainer, Paul main encouragement to the Thessalonican church is that they need to be afraid they have entered into the “last days” and ought to encourage one another and be “strengthened in every good deed and word” (2:16)