What led Paul to write this letter, was undoubtedly the report Timothy brought him respecting the condition of the Thessalonian church. The apostle felt that he had been torn away from them all too soon and had not had sufficient time to establish them in the truth. Hence he was greatly concerned about their spiritual welfare after his forced departure. The coming of Timothy brought him some relief, for he learnt from that fellow-laborer that the church, though persecuted, did not waver, and that their faith had become an example to many. Yet he was not entirely at ease, since he also heard that the Jews were insinuating that his moral conduct left a great deal to be desired, while he had misled the Thessalonians for temporal gain and vainglory, 2:3-10; that some heathen vices were still prevalent in the church; and that the doctrine of the parousia had been misconstrued, giving some occasion to cease their daily labors, and others, to feel concerned about the future condition of those who had recently died in their midst. That information led to the composition of our Epistle.
In view of all these things it was but natural that the apostle should have a threefold purpose in writing this letter. In the first place he desired to express his gratitude for the faithful perseverance of the Thessalonians. In the second place he sought to establish them in faith, which was all the more necessary, since the enemy had sown tares among the wheat. Hence he reminds them of his work among them, pointing out that his conversation among them was above reproach, and that as a true apostle he had labored among them without covetousness and vainglory. And in the third place he aimed at correcting their conception of the Lords return, emphasizing its importance as a motive for sanctification,
There is little uncertainty as to the time and place of composition, except in the ranks of those who regard the Epistle as a forgery. When Paul wrote this letter, the memory of his visit to Thessalonica was still vivid (1:1-10 and 2:1-20); and he was evidently in some central place, where he could keep posted on the state of affairs in Macedonia and Achaia (1:7-8), and from where he could easily communicate with the Thessalonian church. Moreover Silas and Timothy were with him, of which the former attended the apostle only on his second missionary journey. and the latter could not bring him a report of conditions at Thessalonica, until he returned to the apostle at Corinth, Acts 18:5. Therefore the Epistle was written during Paul’s stay in that city. However it should not be dated at the beginning of Paul’s Corinthian residence, since the faith of the Thessalonians had already become manifest throughout Macedonia and Achaia, and some deaths had occurred in the church of Thessalonica. Neither can we place it toward the end of that period, for II Thessalonians was also written before the apostle left Corinth. Most likely it was composed towards the end of A. D. 52.
In this letter we behold Paul, the missionary, in the absence of any direct controversy, carefully guarding the interest of one of his most beloved churches, comforting and encouraging her like a father. He strengthens the heart of his persecuted spiritual children with the hope of Christ’s return, when the persecutors shall be punished for their evil work, and the persecuted saints, both the dead and the living, shall receive their eternal reward in the Kingdom of their heavenly Lord. And thus the apostle is an example worthy of imitation; his lesson is a lesson of permanent value. The glorious parousia of Christ is the cheering hope of the militant church in all her struggles to the end of time.
John Piper, Look at the Book: 1 Thessalonians.