PAUL wrote this to the people to be ready for the return on Christ in 51 AD

"For this reason you also must be ready; for the Son of Man is coming at an hour when you do not think He
will." Matthew 24:44

Thessalonia is in Southeastern Europe, north of Greece.

Paul was on his second missionary journey, to check up on and build up churches he established on his first
missionary journey, when he had a vision to go to Macedonia/Thessalonia. Thessalonia was predomintly a
traditional Jewish establishment. The Jews there really didn't accept him and his teachings, and Paul had to
leave. Eventually he ended up in Corinth in southern Greece (Acts-2Corinthians). It's in Corinth that he
writes to the Thessalonians.

He describes the second coming of Christ (and the resurrection of the saints) in detail.
He describes "sanctified living" to prepare and purify yourself for the second coming.
He encouraged them to leave their "pagan" lifestyle, to give up the "temple prostitutes" (using sex & the
prostitutes to get the men to go to their temple).
Preparing for the end.

It's a portrait of yourself. You're surrounded by a wrong doing secular society, controlled in part by satan.
It's always a temptation to return to a worldly "lifestyle" that is wrong.
Understand the rapture, and other knowledge of the end times, so that it gives you confidence.
Study it to PREPARE for the end, and the return of the Lord. You don't know when the Son of Man will come.