Brothers and sisters, we do not want you to be uninformed about those who sleep in death, so that you do not grieve like the rest of mankind, who have no hope. For we believe that Jesus died and rose again, and so we believe that God will bring with Jesus those who have fallen asleep in him. According to the Lord’s word, we tell you that we who are still alive, who are left until the coming of the Lord, will certainly not precede those who have fallen asleep. 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.
1 Thessalonians 4:13-17 (circa AD 49-51)
Paul said that because Jesus died and rose from the dead others would too. How does this follow?
He also claimed that all a person had to do to be sure of a spiritual resurrection was to believe that Jesus had already risen (1 Corinthians 15:20, AD 53-54), How did he know this? Almost certainly it came to him in one of his visions and his subsequent ‘revelations’ (‘the Lord’s word’ as he puts it in the letter to the Thessalonian sect).
Possibly, though less likely, he learnt it from the Christians he persecuted prior to his conversion. If so, where did they get the idea from? That the cult members in Thessalonica had to ask Paul what would happen to those who had passed away suggests this wasn’t a significant concern prior to this point. Paul and other early believers thought the Messiah/Son of Man was going to appear within their lifetimes (‘we who are still alive’ etc). It was only when cultists started dying off in noticeable numbers, and the Lord remained a no-show, that it started to become an issue. Paul had to make something up. And make it up he did.