Although the thrust of the letter is varied, the subject of eschatology (doctrine of last things) seems to be predominant in both Thessalonian letters. Every chapter of 1 Thessalonians ends with a reference to the second coming of Christ.
This epistle is generally considered to have been the first of those written by St. Paul. The occasion seems to have been the good report of the steadfastness of the church at Thessalonica in the faith of the gospel. It is full of affection and confidence, and more consolatory and practical, and less doctrinal, than some of the other epistles.Matthew Henry