First of all, the subject of the book of Thessalonians is an address to a congregation experiencing intense persecution (1Thes.2:14). Upon Paul’s preaching in this city, many believed, which caused the fanatical Jews to stir up mob violence against him and Jason who housed him. Through a tight security Jason was saved while the brethren sent Paul away secretly in the night to Beroea (Acts17:1-10). Aside of the great persecution that the church went through (1Thes.2:14), they also experienced great sorrow over the loss of a number of their brethren through death (1Thes 4:13).
In order for Paul to strengthen them, he sent Timothy there after his failure to go there twice (1Thes 2:17,-3:3). Upon receiving the encouraging report of Timothy about the brethren, Paul rejoiced (1 Thes.3:6-10). But on a more serious note, they needed further encouragement and strengthening, therefore he had to commend them (1Thes 1:2-10, 2:14; 3:6-10), that they may follow the course approved by God (1Thes 4:1,2), abstain from fornication (1Thes.4:3-8), etc; But above all, that they be comforted with THE RESURRECTION HOPE “But I would not, have you to be ignorant, brethren, concerning THEM WHICH ARE ASLEEP, THAT YE SORROW NOT, even as others which have no HOPE—“ 1Thes.4:13-18.
Therefore the issue in question is that of THE RESURRECTION HOPE and not a ‘RAPTURE’. The word of the Lord in Vs 18 is “wherefore comfort one another with these words” which has to do with the Resurrection of the different categories of the saints Vs 3. Those who “SLEEP IN JESUS” (V.14), those “which are ALIVE and REMAIN” (V. 15,17), and those who are “DEAD IN CHRIST (V. 16). That is to say the saints should not be in sorrow, for all saints shall meet with the Lord through the process of the Resurrection. So the discussion here is not to escape from the persecution of a so called Antichrist in the great tribulation through the Rapture.