As it is noticed in the introduction of the first letter, the two letters that Paul wrote to the Thessalonians belong to the first inspired letters that he wrote. He wrote the first letter as a supplement to what he had already said to them orally. In that way he provided them with the knowledge they were in need of.
The second letter has apparently been written not long after the first one. Those addressed are still young in the faith and therefore easy to be deceived by false teachers, especially with regard to questions about the coming of the Lord. Against the work of the enemy Paul assures them in this letter that the day of the Lord has not come yet. His second letter is therefore correcting. He unmasks the false doctrine and prevents that their faith will suffer shipwreck. False doctrines, including that on the return of Christ, always undermine the faith. On top of that, false doctrines also unchangeably lead to a wrong practice.
The central theme in both letters is the return of Christ. In the first letter questions are being dealt with about the passed away believers. In that letter Paul speaks about the mystery of the rapture of the church and the Old Testament believers. First the believers are caught up into heaven and afterward they form the company of the Lord Jesus when He returns to the earth. First the Lord will come for His own, then He will come with His own. When He appears with His own, the full day of the millennial kingdom of peace, about which many prophets wrote, will dawn.
In the second letter questions are dealt with regarding the living believers on earth. The reason is that there was commotion about the tribulation that they were suffering. They had heard wrong explanations about it. That had caused them to become insecure. They had heard that tribulations belong to the day of the Lord, something that is right in itself. However, the false teachers misused this and said: ‘Our tribulations are the proof that the day of the Lord has come.’ In this second letter Paul will explain what that particular day means. Because this subject is important to the believers of the church of all times, God took care that this letter has been included in the Bible.
The main theme of the letter, which is just mentioned, has the central place. Next to that Paul will also deal with the wrong practice of some who did not want to work for their livelihood. Such believers damage the Christian testimony which the Thessalonians want to form. This behavior has to be corrected. Paul gives instructions how to do that. He opens and closes his letter with a blessing.