1Now, brothers, concerning the coming of our Lord Jesus Christ and our gathering together to him, we ask you 2not to be quickly shaken in your mind or troubled, either by spirit or by word or by letter as if from us, saying that the day of Christ has already come. 3Let no one deceive you in any way. For it will not be unless the rebellion comes first, and the man of sin is revealed, the son of destruction. 4He opposes and exalts himself against all that is called God or that is worshiped, so that he sits as God in the temple of God, setting himself up as God. 5Don’t you remember that when I was still with you, I told you these things? 6Now you know what is restraining him, to the end that he may be revealed in his own season. 7For the mystery of lawlessness already works. Only there is one who restrains now, until he is taken out of the way. 8Then the lawless one will be revealed, whom the Lord will kill with the breath of his mouth and destroy by the manifestation of his coming; 9even he whose coming is according to the working of Satan with all power and signs and lying wonders, 10and with all deception of wickedness for those who are being lost, because they didn’t receive the love of the truth, that they might be saved. 11Because of this, God sends them a powerful delusion, that they should believe a lie, 12that they all might be judged who didn’t believe the truth, but had pleasure in unrighteousness.
13But we are bound to always give thanks to God for you, brothers loved by the Lord, because God chose you from the beginning for salvation through sanctification of the Spirit and belief in the truth, 14to which he called you through our Good News, for the obtaining of the glory of our Lord Jesus Christ. 15So then, brothers, stand firm and hold the traditions which you were taught by us, whether by word or by letter.
16Now our Lord Jesus Christ himself, and God our Father, who loved us and gave us eternal comfort and good hope through grace, 17comfort your hearts and establish you in every good work and word.
Word Study: Coming (Gk. ἀποστασία, apostasia). (2:3; Acts 21:21*) Strong’s 646
This word is only used twice in the NT. It is a compound noun, formed from the preposition ἀπό (apo), “away from,” and στάσις (stasis), “existence, state of being, departure, uprising, rebellion, or strife," depending on the context.” In Acts 21:21, the word refers to forsaking Moses and the Law. In this verse, it may refer to a rebellion, or abandonment. When the word speaks of rebellion or defection, the context indicates against or from what or whom. The text at hand is more difficult since a rebellion or defection is not obvious. One of two options is possible in the context. One, that ἀποστασία (apostasia) refers to a rebellion or apostasy, particularly one led by the “man of sin.”
Another option is that the word should be translated “departure” and speaks of the departure to be with Christ, presented in 2:1. This meaning seems to fit the context of the two letters to the Thessalonians, which focuses on the coming of Jesus in each chapter of 1 Thessalonians, and this emphasis in 2 Thessalonians 2:1. It is true that the Greek word apostasia in the literature of the fathers in the second century use the word of defection from the faith, but the Greek word itself simply means "departure," and then the question becomes "departure" from what.
Even if one takes the word as “apostasy,” the question arises as to the cause of the apostasy. If one expects the rapture before the coming of Christ, it is easy to argue that the church leaving with its indwelling Holy Spirit would reasonably incite a “rebellion” or “apostasy.” This is consistent with 2 Thess 2:6-8, and the “restrainer” being “taken out of the way,” if the “restrainer” is the Holy Spirit, or the church, or most likely, the church indwelled by the Holy Spirit.