Here is the pressing subject matter that Paul addresses to the Thessalonian Church. Since liars (antichrists) were among them and deceived some into believing Christ had already returned and left them behind, Paul sent words to comfort the saints, telling them the Lord had not come, that they must patiently await His coming again. And that certain things would come before the Lord returned the second time.
1 Thessalonians 1:10 (KJV) And to wait for his Son from heaven, whom he raised from the dead, even Jesus, which delivered us from the wrath to come.
1 Thessalonians 2:19 (KJV) For what is our hope, or joy, or crown of rejoicing? Are not even ye in the presence of our Lord Jesus Christ at his coming?
Paul assures the saints those who have already died will return with Christ and then whoever is alive in Christ at that time will be caught up to meet Christ and the returning saints in the air when He descends from heaven with the sounding of the trump of God. The dead in Christ will be caught up first then those living caught up with them forever.
1 Thessalonians 4:13-18 (KJV) 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. For if we believe that Jesus died and rose again, even so them also which sleep in Jesus will God bring with him. For this we say unto you by the word of the Lord, that we which are alive and remain unto the coming of the Lord shall not prevent them which are asleep. For the Lord himself shall descend from heaven with a shout, with the voice of the archangel, and with the trump of God: and the dead in Christ shall rise first: Then we which are alive and remain shall be caught up together with them in the clouds, to meet the Lord in the air: and so shall we ever be with the Lord. Wherefore comfort one another with these words.
The day of the Lord would not come as a thief in the night for those who are looking for His coming again. But for those in darkness that day will come with DESTRUCTION with NO ESCAPE.
1 Thessalonians 5:1-5 (KJV) But of the times and the seasons, brethren, ye have no need that I write unto you. For yourselves know perfectly that the day of the Lord so cometh as a thief in the night. For when they shall say, Peace and safety; then sudden destruction cometh upon them, as travail upon a woman with child; and they shall not escape. But ye, brethren, are not in darkness, that that day should overtake you as a thief. Ye are all the children of light, and the children of the day: we are not of the night, nor of darkness.
Paul tells us when the Lord Jesus is revealed from heaven with His mighty angels IN FLAMING FIRE taking vengeance on them that do not know God, who will be PUNISHED with EVERLASTING DESTRUCTION but glorified in His saints.
2 Thessalonians 1:7-10 (KJV) And to you who are troubled rest with us, when the Lord Jesus shall be revealed from heaven with his mighty angels, In flaming fire taking vengeance on them that know not God, and that obey not the gospel of our Lord Jesus Christ: Who shall be punished with everlasting destruction from the presence of the Lord, and from the glory of his power; When he shall come to be glorified in his saints, and to be admired in all them that believe (because our testimony among you was believed) in that day.
You quote the following passage of Scripture but left out the timing for these verses is "by the coming of our Lord Jesus Christ, and our gathering together unto Him". Paul says don't believe those who tell you the day of Christ is at hand because there will first be a falling away and the man of sin is revealed as the son of perdition (antichrists). Paul had already warned them of this. Because the mystery of iniquity was already at work among them and would be until the Church is taken up with the Lord, and then the wicked will be destroyed by the brightness of His coming.
2 Thessalonians 2:1-12 (KJV) Now we beseech you, brethren, by the coming of our Lord Jesus Christ, and by our gathering together unto him, 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. 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; 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. Remember ye not, that, when I was yet with you, I told you these things? And now ye know what withholdeth that he might be revealed in his time. For the mystery of iniquity doth already work: only he who now letteth will let, until he be taken out of the way. And then shall that Wicked be revealed, whom the Lord shall consume with the spirit of his mouth, and shall destroy with the brightness of his coming: Even him, whose coming is after the working of Satan with all power and signs and lying wonders, And with all deceivableness of unrighteousness in them that perish; because they received not the love of the truth, that they might be saved. And for this cause God shall send them strong delusion, that they should believe a lie: That they all might be damned who believed not the truth, but had pleasure in unrighteousness.