Note 1 at 2 Th. 2:1: Paul had spoken about the second coming of the Lord Jesus Christ in his previous letter to the Thessalonians. Most of his remarks about that subject centered around comforting the believers over their loved ones who had died (1 Th. 4:13-18).

However, in 1 Thessalonians 5:1-4, Paul did speak about the time in which the Lord would come back. He made it very clear that no man could know the exact time of Christ's return (1 Th. 5:2), but he did caution them to be ready. Apparently, that led some of the Thessalonians to fear that Christ's second coming was imminent. Paul is now trying to straighten their thinking out on this issue.

Paul gives two things that will happen before Christ returns. First there has to be a falling away (see note 6 at v. 3, p. 1252) and secondly, "that man of sin" has to be revealed (see note 7 at v. 3, p. 1252).