What is the apostasy, the man of lawlessness, the mystery of lawlessness, and the restrainer that will be taken out of the way that the apostle Paul refers to in the letter below?
Now we request you, brethren, with regard to the coming of our Lord Jesus Christ and our gathering together to Him, that you not be quickly shaken from your composure or be disturbed either by a spirit or a message or a letter as if from us, to the effect that the day of the Lord has come. Let no one in any way deceive you, for it will not come unless the apostasy comes first, and the man of lawlessness is revealed, the son of destruction, who opposes and exalts himself above every so-called god or object of worship, so that he takes his seat in the temple of God, displaying himself as being God. Do you not remember that while I was still with you, I was telling you these things? And you know what restrains him now, so that in his time he will be revealed. For the mystery of lawlessness is already at work; only he who now restrains will do so until he is taken out of the way. Then that lawless one will be revealed whom the Lord will slay with the breath of His mouth and bring to an end by the appearance of His coming; that is, the one whose coming is in accord with the activity of Satan, with all power and signs and false wonders, and with all the deception of wickedness for those who perish, because they did not receive the love of the truth so as to be saved. For this reason God will send upon them a deluding influence so that they will believe what is false, in order that they all may be judged who did not believe the truth, but took pleasure in wickedness.
(2 Thessalonians 2:1-16 NASB)