13But we do not want you to be uninformed, brethren, about those who are asleep, so that you will not grieve as do the rest who have no hope. 14For if we believe that Jesus died and rose again, even so God will bring with Him those who have fallen asleep in Jesus.15For this we say to you by the word of the Lord, that we who are alive and remain until the coming of the Lord, will not precede those who have fallen asleep.16For the Lord Himself will descend from heaven with a shout, with the voice of the archangel and with the trumpet of God, and the dead in Christ will rise first. 17Then we who are alive and remain will be caught up together with them in the clouds to meet the Lord in the air, and so we shall always be with the Lord. 18Therefore comfort one another with these words.
Apparently, the Thessalonians needed to be reassured about what happens to believers after they die. Paul explained the truth to them to give them comfort and hope in the awesome future we have in Christ, whether we die or are alive before He comes. "Now we can comfort one another with these words."