Paul gives instructions for holy and godly living (as he often does) and then encourages them with the hope of the resurrection of the dead and living with Christ!
It is God's will that you should be sanctified: that you should avoid sexual immorality; not in passionate lust like the pagans, who do not know God;
1 Thessalonians 4:3, 5
Here are some of the holy living commands. He also talks about loving one another more and more - godly living.
For the Lord himself will come down from heaven, with a loud command, with the voice of the archangel and with the trumpet call of God, and the dead in Christ will rise first. After that, we who are still alive and are left will be caught up together with them in the clouds to meet the Lord in the air. And so we will be with the Lord forever. Therefore encourage one another with these words.
1 Thessalonians 4:16-18 NIV
An end- time description of what will happen when Christ returns. The dead in Christ will rise and those in Christ still living will join Christ in the clouds and both will live with him forever.