The eighth of Paul's Epistles is I Thessalonians. It was written by Paul when he was in Corinth or Athens, approximately 51 AD, making it the oldest of the books in the New Testament.
Thessalonica was in Northern Greece, where Paul had spent some time. His message of salvation through Christ was popular amongst the Gentiles there, and this had aroused the anger of the Jewish population and they had turned against Paul. To escape the mob, Paul had to flee during the night.
Concerned for the Christians in Thessalonica, Paul had sent his friend Timothy there, to see how they were getting on. Timothy met up with Paul in Corinth, giving an encouraging report on the Thessalonian Church, to which this letter is a response.