Ok, it seems that the issue is one of interpretation, as usual.
16 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. 17 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. 18 Therefore encourage one another with these words. (1 Thessalonians 4- NIV)
Who is "we"? Does Paul refer to Him and the Thessalonians or believers that are still alive at the time?
It seems to me, and mnay others, that Paul wrote the 2nd letter to clear up an obvious misunderstanding that was circulating, perhaps even started by Him by a misunderstanding of what was teaching.
Since in NO OTHER of his letters do we find Paul saying the end will came in His lifetime we can assume that the confusion was from the Thessolonian's part and it may have been how Paul worded it, as is a prime example of the above.
The Coming of the Lord
13 But we do not want you to be uninformed, brothers and sisters, g about those who have died, h so that you may not grieve as others do who have no hope. 14 For since we believe that Jesus died and rose again, even so, through Jesus, God will bring with him those who have died. i 15 For this we declare to you by the word of the Lord, that we who are alive, who are left until the coming of the Lord, will by no means precede those who have died. j 16 For the Lord himself, with a cry of command, with the archangel’s call and with the sound of God’s trumpet, will descend from heaven, and the dead in Christ will rise first. 17 Then we who are alive, who are left, will be caught up in the clouds together with them to meet the Lord in the air; and so we will be with the Lord forever. 18 Therefore encourage one another with these words.
5 Now concerning the times and the seasons, brothers and sisters, a you do not need to have anything written to you. 2 For you yourselves know very well that the day of the Lord will come like a thief in the night. 3 When they say, “There is peace and security,” then sudden destruction will come upon them, as labor pains come upon a pregnant woman, and there will be no escape! 4 But you, beloved, b are not in darkness, for that day to surprise you like a thief; 5 for you are all children of light and children of the day; we are not of the night or of darkness. 6 So then let us not fall asleep as others do, but let us keep awake and be sober; 7 for those who sleep sleep at night, and those who are drunk get drunk at night. 8 But since we belong to the day, let us be sober, and put on the breastplate of faith and love, and for a helmet the hope of salvation. 9 For God has destined us not for wrath but for obtaining salvation through our Lord Jesus Christ, 10 who died for us, so that whether we are awake or asleep we may live with him. 11 Therefore encourage one another and build up each other, as indeed you are doing.