"The First Epistle to the Thessalonians, usually referred to simply as First Thessalonians and often written 1 Thessalonians, is a book from the New Testament of the Christian Bible," according to Wikipedia.
"The first letter to the Thessalonians was probably the first of Paul's letters, probably written by the end of AD 52, making it the oldest book in the New Testament.
"Most New Testament scholars believe Paul the Apostle wrote this letter from Corinth, although information appended to this work in many early manuscripts (e.g., Codices Alexandrinus, Mosquensis, and Angelicus) state that Paul wrote it in Athens after Timothy had returned from Macedonia with news of the state of the church in Thessalonica (Acts 18:1–5; 1 Thes. 3:6).
"For the most part, the letter is personal in nature, with only the final two chapters spent addressing issues of doctrine, almost as an aside.
"Paul's main purpose in writing is to encourage and reassure the Christians there. Paul urges them to go on working quietly while waiting in hope for the return of Christ."