The passage
      v1. Paul describes the last day as a "coming" of Jesus and a gathering together of believers, Matt.24:31.
      v2. Concerning the second coming, Paul does not want his readers led astray by false teachings which claim that the "day of the Lord has already come", cf. 1Thess.5:2.
      v3. Paul makes the point that "the day" hasn't already come because certain preliminary events have not yet occurred. There must first be the "rebellion". This is a time of great apostasy, a rebellion of both church and state against God. Then the "man of lawlessness" must be revealed. This "man", Mr. Loss, is most likely the antichrist. He is the one who is doomed to destruction, but first he must be revealed.
      v4. The antichrist is the one who "opposes" God, exalts himself over God and claims deity for himself.
      v5. Paul had already told his readers all this when he was with them. If only we knew what he had actually told them!
      v6-7. At the present moment, the antichrist rules quietly, awaiting the day of his revealing. The reference to "the restrainer", the one holding him back, is a misreading of the Greek.
      v8. In the final day the antichrist will be revealed in all his horror, and once he displays his real self he will be destroyed by Christ. His revealing is imaged in the revealing of the beast who, in coming out of the primeval bog, displays the pure horror of his person, Dan.7, Rev.13. Jesus, at his second coming, will destroy him with a word.
      v9. Jesus will come with splendor, but the antichrist also has a "coming" (the same word is used for Jesus' coming) and it too will be in splendor. The display of his glorious power is described in the same terms used of Jesus' demonstrations of power. The antichrist comes as Satan's representative, cf. Rev.13.
      v10-12. The coming of the antichrist will deceive many. Many will follow him, and it is most likely that the deceived ones will include church members, cf. Matt.24:24. They are deceived because they do not possess the truth of the gospel; false teaching has undermined their salvation. God then acts in judgement to accentuate their rebellion by deluding them. The result of the delusion is that those who follow the antichrist will receive the judgement due them.

The Man of Lawlessness
      When Paul writes his second letter to the church at Thessalonica, he is writing to a church totally focused on the second coming of Christ. Some of the members had even given up their jobs and were sitting around waiting for the day of Christ's return. So, Paul lets them into a secret. Before Jesus comes there will be the rebellion and the coming of the man of lawlessness. This evil man, the man of sin, Mr. Loss, is even now causing trouble. Yet, it's only when he fully breaks loose that the end is upon us. In Paul's day, as in our day, Mr. Loss is around causing us some pain, but he is not in full-blown destruction mode, he is not revealed ("coming") in all his glory.
      Mr. Loss, revealed elsewhere in the scriptures as the antichrist, is rather difficult to identify because he takes on many shapes. He can be a political leader, a philosophy, a heresy, a revolutionary group...... yes the day may even come when he is a rouge computer.
      Paul says that "the secret power of lawlessness is already at work", although yet to be "revealed." So, what is he up to right now, what is he doing?
        First, he opposes and exalts himself over everything that is God's. He intrudes his evil into the fellowship of believers and claims of himself the status of God, v4. This is why he is often a heresy articulated by fanatics.
        Second, he is running the secular agenda. Verses 6 and 7 seem to suggest that there is something or someone restraining his present activities, but this is most likely a translation problem. The word "restrain" can actually be translated "rule". So, it is more likely that Paul is saying that the antichrist is actually running things for the present. Remember, Satan has "the whole world in his hand" cf. Luke.4:5-8. None-the-less, the day is coming when he will break out in total evil.
        Third, he deludes humanity, including believers, v9-12. His "coming", or manifestation, is similar to Christ's coming. He comes with "miracles, signs and wonders", but they are "counterfeit" and "evil". His focus is on those who are not confident in their salvation. At first reading, those who have "refused to love the truth and so be saved" may seem like godless pagans, but the description most likely includes "apostate" believers. Their salvation is undermined because they do not rest on gospel truth; they have "not believed the truth." Their delusion prepares them for the judgement of God in the day when Mr. Loss finally displays himself.
      So there he is, Mr. Loss. There is only one place of safety in the presence of the antichrist and this is at the foot of the cross.

v1
      parousiaV (a) "coming" - "The coming of a hidden deity who makes his presence felt by a revelation of his power", BAGD. Paul encourages his readers not to misunderstand the teaching he gave them while he was with them. The second coming is close, but has not "already come."
      episunagwghV (h) "gathered" - gather together, assembling with. Interestingly, the writer to the Hebrews uses the same word to describe the gathering of believers for worship, Heb.10:25. Our gathering with Christ for worship reflects our gathering with him in the day of his return.

v2
      Paul seems unsure where the wrong ideas have come from. False teachers may be the source. Like any preacher he would hope that he himself was not the source of the confusion. The church was certainly concerned about the timing of Christ's return.
      enesthken (enisthmi) perf. "has already come" - has come. Rather than actually "come", the phrase is better translated "is close at hand", or "is as good as here." This is why some of the Thessalonians have given up their jobs.

v3
Extended Note: the man of lawlessness
      The "man of lawlessness", traditionally known as "the man of sin", is usually identified as the antichrist. Our biggest problem is to get a clear picture of him. He is often seen as the Roman Emperor, or even Rome itself. In the Preface of the Authorized Version of the Bible the Pope is called "that Man of Sin", a rather sad example of religious bigotry (as an Anglican myself it is reasonable for me to make that comment). Numerous political leaders and powers have been identified as this "man". He is described as the "man doomed to destruction", the doomed one, Mr. Loss. Judas was described as the doomed one. Paul writes as if this "man" is already around, although yet to be revealed. The difficulty with identification, particularly when we identify him with people etc. we don't agree with, indicates that he is most likely chameleon-like. He does his thing in different guises. He can even be an idea. So what is his "thing", his "bag"?
      He is the one who "opposes" God, exalts himself over God and claims deity for himself. He sets himself up in the temple and in that sense enacts Jesus' prophesy of the "abomination of desolation", Mark 13:14. The abomination is prophesied in the book of Daniel and is best translated as "the abomination that causes horror." Jesus tells us that this is the sign which should cause us to flee to safety in the last day. The image may refer to the time when the temple was defiled by Antiochus IV Epiphanes 175-164 BC. He entered the holy of holies and plundered the temple. He then set up an idol in the temple and halted the religion of Israel. The Roman emperor Caligula threatened to do the same thing in 40AD. The image may be of foreign powers attacking the people of God, plundering Jerusalem and the temple. The Babylonians and the Romans certainly did this. Some translate Matt.24:15 as "the sign of the abomination", referring to the Roman ensign. The destruction of Jerusalem in 70AD would then be a partial fulfillment of this prophecy. For us today, the temple is the Christian church, 1Cor.3:16f. Mr. Loss will therefore "desolate" the fellowship of believers. This may involve external persecution or internal apostasy, and most likely both.
      It is obviously important for us to identify who this man of lawlessness is and what he is up to. There are a couple of reasons why we need to do this:
      First, he is extremely powerful, wondrous even, and the glory he possesses has the capacity to deceive us. He is active now and so he "deceives" us right now. As for the day when he is revealed in all his glory, he will be a "powerful delusion" and many will be sucked in by this "man doomed to destruction". His deception has already affected may believers, undermining their salvation by undermining the "truth".
      Second, he is "coming", and this could be in our lifetime. Being prepared means keeping an eye open for him, but if we don't know him then there is little point looking for him.
      In simple terms, Mr. Loss, the man of lawlessness is the antichrist. He is around at this very moment practicing the things he will do in the last day, although he's not in full-on horror mode at the present. The antichrist is the Devil's friend, the beast from the bog described in Daniel 7 and Revelation 13. He works for Satan. He has shown himself in times past and he will show himself in the future, but in the last day, watch out.
      Paul tells us that he is "doomed to destruction" for at the return of Jesus he will be destroyed with a word from the Lord - Jesus will overthrow him "with the breath of his mouth" and destroy him with "the splendor of his coming." The "lawless one" will be destroyed because he lives "in accordance with the work of Satan."
      In passing, it should be noted that many commentators see the revealing of the man of lawlessness associated with the formation of the modern state of Israel and the rebuilding of the temple. Due to this association, many believers have turned a blind eye to Israel's annexation of Palestinian land and their subjugation of the Palestinian people, 10% of whom are Christians. Although a highly charged issue it needs to be stated firmly that Biblical support for such an interpretation is very thin.

      hJ apostasia "the rebellion" - apostasy. The word "rebellion" means "falling away" in the sense of a falling away from God. Both Lightfoot and Denney see this as referring to the church, cf. Matt.24:10-12. Others see it referring to the Jews, although this is unlikely. Others see it in general terms as a revolt against God, rather than a falling away of the church, although this will be part of picture, cf. Neil. Certainly, the "falling away" will include the apostasy of the Christian church.

v7
      musthrion "secret" - The "secret" is best understood as a mystery now revealed in the gospel.
      oJ katecwn (katecw) pres. part. "the one who [now] holds it back" - the one holding sway, prevailing, ruling. For the present, the antichrist is being held back, restrained, although he is active now. What or who is "that which restrains", or even "he that restrains"? There are numerous possibilities. The Jewish state, the Roman state, the moral order, even good angelic powers. Yet, it is better to translate this term as "occupy a position", "be the top man". The meaning then would be that the man of lawlessness presently exists and rules and soon will break out in full-blown evil.