This is the First Letter which was sent by Paul to the Church at Thessalonica or Salonika. We shall use this shorter name because it is easier!
We read in Acts 17: 1-9 about the beginning of the church at Salonika. This was about AD.51 and perhaps only twenty years after the death and rising again of Jesus. Paul and Silas had been beaten (Acts 16: 22) and put in prison in Philippi because they had spread the Good News about Jesus. Probably they left Luke and Timothy behind in Philippi. After the beating they had received, the 160 km journey on foot to Salonika cannot have been easy. Having been beaten would they now keep quiet about the Good News?
No Christian church had gathered in Salonika up to that time. There may have been some Christians who had moved to the city from other places; we do not know. [0.1] Paul and Silas went to the place of Jewish worship, and for three weeks they taught about Jesus. The people who worshipped there were not all Jews. In those times, many Greeks shared in Jewish worship: they were tired of the worship of false gods. They were looking for something better. When they heard the Good News they knew they had found what they wanted. (Acts 17: 4)
The Jews did not like to see so many people leaving their worship to follow Jesus, so they made trouble. They took some 'bad men from among the market people' and tried to force Paul and Silas to come to a meeting of the people of the city. Jason must have been one of the new Christians: he and others were brought to the 'Politarchs'. They were the five or six men who had authority over the city. After this, Paul and Silas had to leave the city. Their stay had been about six months.
Salonika was founded in the year 315 BC. It has always been an important city. It is in the part of northern Greece, which is called Macedonia. Paul was worried because he had to leave the new church so soon but he could not go back (2: 18). Paul had spread the Good News in Beroea and reached Athens (See Acts 17: 16-34). He sent a message back to Beroea for Silas and Timothy to come to Athens. (Acts 17: 15). Remember that each journey between Corinth and Salonika was over 300 km. Part might be done by sea, but probably it was all done on foot. In 1 Thessalonians 3: 1 we learn that Timothy had joined Paul at Athens. Timothy was then sent back to find out how the church was getting on. In 1 Thessalonians 3: 6 we learn that Timothy has come back again and from Acts 18: 5 we learn that Paul has left Athens and is now in Corinth.
At this point Paul wrote the First Letter to Thessalonica. Most people think that this letter is the first to be written of the letters of Paul in the New Testament. I think Galatians and the Letter from James were written even earlier: many people would not agree. This letter is important in any case because it gives us a picture of the Church so soon after its beginnings. We can think of Paul writing it in the big sheds in Corinth where he worked with Aquila making tents and perhaps sails for ships. He does not use any verses from the Old Testament; this is unusual.