After Paul had written his first letter to the Thessalonians he received word that further confusion had arisen in the church there about the doctrine of the second coming of Christ. Seemingly it was reported that Paul himself had sent the information, or at least was the source of it. In addition to that, some people were thinking that the coming of Christ was so near that it was no longer necessary to support oneself or one's family. Why work if Christ is about to end the world? To deal with those issues, as well as to encourage believers, Paul wrote a second letter, probably within a few months of having written his first letter.

Paul began by encouraging the Thessalonians in the midst of their persecutions. He pointed out that they were called to be worthy of the kingdom of God for which they were currently suffering. If they bore up under it, when Christ returned they would be comforted and their persecutors would feel the judging hand of God. On the day when Christ returns he will be glorified among his saints and will banish from his presence all who have rejected the gospel (1:5-12).
Paul went on to say that the coming of Christ would not take place without some other events happening first. It is a mistake, Paul said, to imagine that the Second Coming can happen without relation to the rest of the plan of God. Christ's return must be preceded by a general falling away (or apostasy); the unveiling of a "man of lawlessness," usually called the Antichrist, and his attempts at universal domination. The Antichrist is already at work in spirit, but he must be manifested as such before the end can come. After these things take place, the Lord Jesus will return to destroy him (2:8).
Paul followed this explanation with ethical exhortations of a practical sort. The doctrine of Christ's coming is not to make us lazy, arrogant, or immoral, but busy, humble, and pure. We are not to be weary in well-doing (3:6-13).