Paul, Silvanius and Timothy all send love and kisses to the church they've established in Thessalonia. Also, they are so, so, glad they will be with them when the apocalypse happens.
Paul reminds the Thessalonians about how he was abused in Phillipi, but still got it together to come to them and convert them through endless proselytizing. And now the Thessalonians themselves are also being abused, just like the Jews persecuted Jesus and have forbidden Paul & co. from hectoring people on the streets. Anyway, Paul promises to visit soon, but right now Satan's keeping him away.
Paul thought the apocalypse was nigh and sent Timothy to make sure the Thessalonians were properly faithful, and he was so, so happy to find out they're good little apocalyptic believers. Godot-like, he promises to visit soon to iron out any small misunderstandings in their faith. Until then, he reminds them to be charitable.
Paul reminds the Thessalonians of the rules he set out on his last visit, namely no fornicating and for god's sake, gentlemen, control your vessel in sanctification and honour (v. 4). Whether your vessel is your wife or your penis is a matter of interpretation and icky either way. Other rules: no stealing, no hatefulness, convert people, work hard and forget about dead people, because you'll see them in heaven.
Nobody knows when doomsday will happen. But the believers will be prepared, whereas the unbelievers will feel the destruction like a woman's labour. Until then, no drinking, be nice to people, and pray.
I love it when entire books can be summarised in under an hour.