Paul taught that 'we would not all sleep (die), but some of us (Christians) would be alive and remain when Christ returns for the Church (the Rapture, not the 2nd Coming). Paul understood the time of his departure, by death, was near and said so. Paul also comforted the Thessalonians that the 'day of the Lord' had not arrived yet, that there would be a 'falling away' first, and the 'man of perdition' - the anti-christ would be revealed before the 2nd Coming.
2:1 Now we beseech you, brethren, by the coming of our Lord Jesus Christ, and by our gathering together unto him, 2:2 That ye be not soon shaken in mind, or be troubled, neither by spirit, nor by word, nor by letter as from us, as that the day of Christ is at hand.
2:3 Let no man deceive you by any means: for that day shall not come, except there come a falling away first, and that man of sin be revealed, the son of perdition; 2:4 Who opposeth and exalteth himself above all that is called God, or that is worshipped; so that he as God sitteth in the temple of God, shewing himself that he is God.
(King James Bible, 2 Thessalonians)
Jesus spoke of all these terrible things, as only 'birth-pangs' for what was to come (The Great Seven Year Tribulation).
Listen to this warning of what it would be like in the Last Days:
3:1 This know also, that in the last days perilous times shall come.
3:2 For men shall be lovers of their own selves, covetous, boasters, proud, blasphemers, disobedient to parents, unthankful, unholy, 3:3 Without natural affection, trucebreakers, false accusers, incontinent, fierce, despisers of those that are good, 3:4 Traitors, heady, highminded, lovers of pleasures more than lovers of God; 3:5 Having a form of godliness, but denying the power thereof: from such turn away.
Seems to me we are getting closer to His Return, possibly in this generation, and I bet I am right!