The apostle Paul's second missionary journey included a visit to the prominent Greek city of Thessalonica. This stood alongside a major land route and boasted a busy seaport. A number of individuals believed Paul's message (Acts 17:1–4), but an angry mob forced Paul to leave the city after his brief stay. Later, while in Athens, Paul received a glowing report: the believers at Thessalonica were growing spiritually and serving God fervently. However, they had questions about the Lord's return, including what happens to a believer who dies before that day. And, as all churches do, they had some areas in which they were falling short. In Paul's first letter to the Thessalonians, written about AD 51, he addresses these developments. Paul expresses gratitude for the Thessalonian believers' spiritual progress, and frequently makes references to Christ's impending return.
(BibleRef)