Since the situation in the Thessalonian church has not changed substantially, Paul’s purpose in writing is very much the same as in his first letter to them. He writes (1) to encourage persecuted believers, (2) to correct a misunderstanding concerning the Lord’s return, and (3) to exhort the Thessalonians to be steadfast and to work for a living.
The second epistle to the Thessalonians was written soon after the first. The apostle was told that, from some expressions in his first letter, many expected the second coming of Christ was at hand, and that the day of judgment would arrive in their time. Some of these neglected their worldly duties. St. Paul wrote again to correct their error, which hindered the spread of the gospel. He had written agreeably to the words of the prophets of the Old Testament; and he tells them there were many counsels of the Most High yet to be fulfilled, before that day of the Lord should come, though, because it is sure, he had spoken of it as near. The subject led to a remarkable foretelling, of some of the future events which were to take place in the after-ages of the Christian church, and which show the prophetic spirit the apostle possessed.Matthew Henry