The letter of Paul to the church in Thessalonica is the very earliest piece of Christian literature we have: it is earliest letter Paul wrote, and earlier than all four gospels. So we have a small glimpse into the spread of the gospel not so long after the death and resurrection of Jesus.
This short letter is filled with thanksgiving for the community, for their reception of the gospel, for their faithfulness. Paul also admonishes them to holy living, and reminds them that he believes that the Lord Jesus is coming soon. Not that they have a time or a date set, but they are waiting eagerly for the return of Jesus. In fact, one of the concerns that the people of Thessalonica have is that they had at first believed that none of them would die before Jesus' return. Now the unthinkable has happened, and a few of the members of their community have died. What are they to think about this?
Paul gives them a picture of what he believes will happen: those who have died, will rise first, and then those who are still alive will go up to meet the Lord in the air. (I suspect that this is where the term "rapture", which is not found in the Bible, originates. I'm not sure why it came to be called "the rapture".) As well, Paul cautions the church members not to grieve "as those who have no hope." Even though some of them have died, they have hope of the new kingdom and the new life God is preparing for them, and preparing them for.
It's unfortunate, but I suppose unavoidable given the context that Paul disparages "the Jews": unavoidable because at this time the chief opposition to the spread of the message of Jesus came from Jewish leaders. It is unfortunate, because rhetoric like this has contributed greatly to great persecution of Jews by Christians throughout many centuries. While we are at it, we might notice that when Paul admonishes the congregation, he also urges them not to be like the Gentiles, "who don't know right from wrong." (By the way, most of us who are reading these letters are Gentiles.)
At the end of the letter, Paul gives many memorable, pithy words of encouragement. Short as haiku, simple and profound, words like "Pray without ceasing" and "Rejoice always" and "Give thanks in every situation" haunt us, because we can remember them.
The Lord may not be coming tomorrow, but the Lord is near. Do not quench the Holy Spirit. Just don't.