When Paul parted from Barnabas (Acts 15:36-41) at the beginning of what is called his second missionary journey, he chose Silvanus (Silas) as his traveling companion. Soon afterwards he took Timothy along with him (Acts 16:1-3). Paul was now clearly at the head of his own missionary band. About A.D. 50, he arrived in Greece for the first time. In making converts in Philippi and, soon afterwards, in Thessalonica, he was beset by persecution from Jews and Gentiles alike. Moving on to Beroea, he was again harassed by enemies from Thessalonica and hurriedly left for Athens (Acts 16:11-17:15). Silvanus and Timothy remained behind for a while. Paul soon sent Timothy back to Thessalonica to strengthen that community in its trials (1 Thes 3:1-5). Timothy and Silvanus finally returned to Paul when he reached Corinth (Acts 18:1-18), probably in the early summer of A.D. 51. Timothy’s return with a report on conditions at Thessalonica served as the occasion for Paul’s first letter (1 Thes 3:6-8).
The letter begins with a brief address (1 Thes 1:1) and concludes with a greeting (1 Thes 5:26-28). The body of the letter consists of two major parts. The first (1 Thes 1:2-3:13) is a set of three sections of thanksgiving connected by two apologiae (defenses) dealing, respectively, with the missionaries' previous conduct and their current concerns. Paul’s thankful optimism regarding the Thessalonians' spiritual welfare is tempered by his insistence on their recognition of the selfless love shown by the missionaries. In an age of itinerant peddlers of new religions, Paul found it necessary to emphasize not only the content of his gospel but also his manner of presenting it, for both attested to God’s grace as freely bestowed and powerfully effected.
The second part of the letter (1 Thes 4:1-5:25) is specifically hortatory or parenetic. The superabundant love for which Paul has just prayed (1 Thes 3:12-13) is to be shown practically by living out the norms of conduct that he has communicated to them. Specific "imperatives" of Christian life, principles for acting morally, stem from the "indicative" of one’s relationship to God through Christ by the sending of the holy Spirit. Thus, moral conduct is the practical, personal expression of one’s Christian faith, love, and hope.
The principal divisions of the First Letter to the Thessalonians are the following:
I. Address (1 Thes 1:1-10)
II. Previous Relations with the Thessalonians (1 Thes 2:1-3:13)
III. Specific Exhortations (1 Thes 4:1-5:25)
IV. Final Greeting (1 Thes 5:26-28)