It is thought that this letter was sent to Thessalonica in A.D. 51, maybe just a couple of months after the first letter. For more background on the city of Thessalonica and the church there, read my introduction to 1 Thessalonians.
[The belief that the Day of the Lord had begun] not only furnished a new argument for the idle but rekindled the fears of the fainthearted. If the Day of the Lord had come, no time remained to acquire the holiness and the faith, hope, and love on which Paul had insisted in his first letter (cf. 1 Thessalonians 3:13; 5:8). The wrath reserved for unbelievers would certainly overtake the Christians as well! When the elders saw that the crisis was more than they could cope with effectively, they sent word to Paul by the first of their number who had occasion to journey to Corinth [where Paul, Silas, and Timothy were] (cf. 2 Thessalonians 3:11, “For we hear that …”).
Paul’s intention was not to introduce new truths but to remind the Thessalonians of the oral instruction the apostle had given while still in their midst (2:5). …
What is particularly significant in this second letter is the role assigned to “tradition” both in the discussion of the day of the Lord and in the treatment of the idle. In the first instance the Thessalonians are urged not to be unsettled in their convictions because of some prophetic utterance or even a letter purporting to be from an apostle (2:1-2); the tradition of teaching delivered to the church remains normative for the testing of doctrine (2:5: cf. 1 Thessalonians 5:21. At the conclusion of chapter 2 Paul writes: “So then, brethren, stand firm and hold to the traditions which you were taught by us, either by word of mouth or by letter” (2:15). Similarly, the offense of the idle in the congregation is twofold: not only were they living in idleness, but their conduct indicated a rejection of “the tradition that you received from us” (3:6). That the second letter is itself a repository of the tradition Paul makes clear when he says: “If any one refused to obey what we say in this letter, note that man, and have nothing to do with him, that he may be ashamed” (3:14). — The New Testament Speaks, by Glenn W. Barker, William L. Lane, and J. Ramsey Michaels — Harper & Row, Publishers (1969)
[When Paul wrote his second letter to the believers in Thessalonica] there was still much among them to be commended. Unlike those at Corinth, they had grown in grace; their faith had “grown exceedingly,” and their love for one another “abounded” (1:3). Not only that, but they were enduring fierce persecution with “patience and faith” (1:4).
When Paul wrote his first letter to them he wrote in part, evidently, to allay their fears that those of their loved ones who had died in Christ might thus miss the Rapture. Explaining the plan of God as to this, he pointed out that the Rapture would include the whole Body of Christ, both living and dead, and that it would precede the Day of the Lord and the outpouring of His wrath.
Evidently erroneous teaching as to this latter was already incipient at Thessalonica at this time, that he should write on it so emphatically as he did in 1 Thessalonians 4 and 5.
By now this teaching had gained ground, however, and with persecution raging, some of them had been led to believe that the Day of the Lord was “at hand” (2:2). Indeed, it seems that a letter had even been forged, to make it appear that Paul himself not taught this.
It may well be that those who thus confused the Thessalonian brethren were Jewish believers. Jewish hopes had been earthly in sphere, and they may well have confused the Rapture with our Lord’s return to reign on earth at the close of the Tribulation. And since Paul evidently expected to be alive at the Rapture (1 Thessalonians 4:17) they apparently concluded that the Day of the Lord had already begun.
It would follow from this, of course, that they would be called upon to endure the most horrible suffering this world has ever known or ever will known until that time (Daniel 12:1; Matthew 24:21). Only after this pouring out of the bowls of God’s wrath, the argument went, would the Lord come to receive His own to Himself.
It is this error that the Apostle refutes in the strongest terms in his second letter to the Thessalonians. — Stam, pages 108-109