After his imprisonment and flogging in Philippi, Paul travelled with Silas and Timothy to Thessalonica and with them, founded a church there. But after three sabbaths of debate in the synagogue, apart from a few Jews who believed Paul's message that Yeshua (Jesus) was the long-awaited Messiah, most of the Jews as a body rejected the gospel Paul preached.
Those Jews who believed and a great number of proselytes, who were not so steeped in the historical Jewish religious dogma of the fathers and therefore more receptive to Paul's teaching, along with not a few of the leading women, joined Paul in the house of Jason, which was next door to the synagogue, where the word of the gospel reached out to the Gentile population.
The seed of the gospel had been sown and found fertile soil, resulting in a church being planted and ministers appointed, and even more amazingly the new converts themselves became missionaries. By both word of mouth and example these new believers were extending the reach of the gospel in Macedonia, Achaia and elsewhere, such was their conviction of the truth of all that Paul had taught them.
Sometime later Paul asked Timothy to return to Thessalonica to continue teaching them the deep truths of the gospel and how to live a life worthy of God. It was Timothy who, joining Paul in Corinth where the letters were written, gave a glowing report of the church there.

Letter 1
Paul starts by complimenting them on their work of faith and labour of love and patience of hope in the Lord Jesus Christ in the sight of our God and Father.
He assessed their relationship and mentions both how he and his companions brought the gospel to them, and their readiness to accept the message. After three sabbaths in the synagogue, a few Jews accepted Paul's message that Jesus was the long-awaited Messiah. However, many proselytes, God fearers were ready to not only hear the word but also receive it and consider its implications. With many of them going with Paul to the house of Jason next door to the synagogue, such was the excitement of this new meaningful gospel to them that leading women of the city and Gentiles were attracted to it also.
Paul challenges them to please God in their daily living, that the message of the gospel is not for belief only, but had to become part of the structure of their lives and the way they went about their daily living. He also comforts them by pointing out the hope of the resurrection, warning them to be prepared for the coming again of the Lord Jesus at any time, which was to keep them on their toes.
Letter 2
In this shorter letter Paul first rejoices in the endurance of the Thessalonians in spite of the persecution they have suffered, for such endurance is a sign of God's righteousness. However, he was concerned about the misunderstanding regarding the second coming of Jesus which had caused some to stop working to prepare themselves for that event.
He tells them that they must not be disturbed by all the news that was going around that the second coming was very near, for no one knows when He will come again, only the Father. And that before his return a great rebellion will occur led by a person who will claim to take the place of God, but Jesus will come and utterly destroy him and his followers.
In the meantime, they should stand firm on the teaching they had received which was the truth of God, in order to receive God's encouragement and secure their hope in Him, to pray for strength in their faith, their work for God and the spreading of the gospel message.
He ends with personal greetings and a benediction.