Paul wrote the Second letter to the Thessalonians around 51 A.D. The theme of the book is the second coming of Jesus Christ. The people of this church were confused because they had accepted a claim that the 'the day of the Lord' had already come and gone. They thought they had missed it and didn't know what they were supposed to do. They were very concerned and probably discouraged. In addition, there were those among them who were idle, folks not working and earning their way. This may have been because of the 'day of the Lord' discouragement or just lazy folks living off the those with more money. In addition to these two issues the Thessalonians were being persecuted so they were feeling beaten down. Paul writes to encourage them in the Lord and let them know 'the day of the Lord' was coming. He also corrects those who aren't working for a living.
The city of Thessalonica was the capital of Madedonia. It was on an east-west highway and became a political and commercial hub. It became known as the 'Mother of all Macedonia' because of its importance to the area. The population in Paul's day was about 200,000 people.