Ye are witnesses, and God also, how holily and justly and unblameably we behaved ourselves among you , 2:10
Trivia: What prevented Paul from visiting the Thessalonians?
Paul predicts that the Jesus will return in his lifetime. He will descend from heaven, the dead will rise, and believers will meet him in the air. This is the main scriptural basis for the "rapture" although that word is not used in the passage or anywhere else in the Bible. (See Mt 24:40-41 for the other source for the rapture.)