Whole chapter discussed by Martin Luther —
The Man of Lawlessness
1Now concerning the coming of our Lord Jesus Christ and our being gathered together to Him, we ask you, brothers, 2not to be easily disconcerted or alarmed by any spirit or message or letter seeming to be from us, alleging that the Day of the Lord has already come. 3Let no one deceive you in any way, for it will not come until the rebellion occurs and the man of lawlessness—the son of destruction—is revealed. 4He will oppose and exalt himself above every so-called god or object of worship. So he will seat himself in the temple of God, proclaiming himself to be God.
5Do you not remember that I told you these things while I was still with you? 6And you know what is now restraining him, so that he may be revealed at the proper time. 7For the mystery of lawlessness is already at work, but the one who now restrains it will continue until he is taken out of the way. 8And then the lawless one will be revealed, whom the Lord Jesus will slay with the breath of His mouth and annihilate by the majesty of His arrival.
9The coming of the lawless one will be accompanied by the working of Satan, with every kind of power, sign, and false wonder, 10and with every wicked deception directed against those who are perishing, because they refused the love of the truth that would have saved them. 11For this reason God will send them a powerful delusion so that they believe the lie, 12in order that judgment may come upon all who have disbelieved the truth and delighted in wickedness.
Stand Firm
13But we should always thank God for you, brothers who are loved by the Lord, because God chose you from the beginning to be saved by the sanctification of the Spirit and by faith in the truth. 14To this He called you through our gospel, so that you may share in the glory of our Lord Jesus Christ. 15Therefore, brothers, stand firm and cling to the traditions we taught you, whether by speech or by letter.
16Now may our Lord Jesus Christ Himself and God our Father, who by grace has loved us and given us eternal comfort and good hope, 17encourage your hearts and strengthen you in every good word and deed.