This is a letter in the Bible's New Testament. Paul wrote it to Christians in Thessalonica not long after his first letter to them.
People were behaving in a cruel way towards the Christians there. Paul told them have confidence in God. When Jesus returned God would punish those wicked people. He would also punish everybody who did not accept the good news about Jesus.
Some Christians in Thessalonica thought that Jesus had already returned. Paul said that the Wicked One would come first. He would oppose Jesus. So, Christians should trust God, even when they suffer. Other Christians in Thessalonica thought that Jesus was coming back very soon. So, they refused to work. Paul reminded them that he himself worked hard in Thessalonica. And they all must work too.