The believers in Thessalonica, already instructed about the Coming of the Lord for the Church (1st Thessalonians 4:13-17), were being troubled by false teachers, who said the Day of the Lord had already arrived. This would mean, for them, that the Lord Jesus would have already come down from heaven and raptured the Church (according to the teaching in the first letter, chapter 4) and so there would be no more hope for them, but of going through the Great Tribulation and suffering the persecutions of the Beast (Matthew 24:15, Daniel 12:1, Revelation 13).
In this chapter 2, Paul refutes such teaching, showing that there will be two important events before that Day: a great apostasy within the churches and the revelation of the man of sin, the “son of perdition" (v.3).
There were disturbers in Thessalonica who were trying to divert the believers from their hope concerning the Coming of the Lord, which Paul had proclaimed in his first letter. The disturbers claimed that a "spirit" or a preaching ("word") or even a special letter from Paul had announced that the day of Christ had come - that period of great judgments and demonstrations of God's wrath against the nations which rejected the Gospel in this current period of the grace of God.
Note that the “Day of the Lord" refers to a period of tribulations and wars, until the descent of the Lord Jesus with the Church to institute the millennium on earth. We understand that the coming of the Lord for the Church (as taught in 1 Thessalonians 4:13-17) will mark the beginning of the period called the Day of the Lord.
He will be a man, possibly an incarnation of Satan - the king of Daniel 11:36 and the "Beast" of Revelation 13:1-8 and 19:19-20. Along with his followers and ministers, he will do "signs and wonders" (see Matthew 24:24), deceiving those who reject the Gospel (see verses 10 to 12 of our passage). He will demand divine worship (v.4) and prohibit any other worship, under penalty of death (Revelation 13:14-15); he will be supported by the "false prophet", the "second Beast" of Revelation 13:11-16.
The operation or influence of the Lawless One is already in the world, for in the days of the apostle there were false teachers, calling themselves Christians, but denying the foundations of faith and trying to divert the believers astray (v.7).
In our days, this "apostasy" is increasingly evident (v.3), with so many heretical sects infiltrating Christianity, and so much fundamentally wrong teaching being delivered by the "ministers of the Word" in many denominations. See 1 Timothy 4:1-3; 2 Timothy 2:15-18; 2 Peter 2:1, 10, 15 and Judas 3-4. The apostle John also warns us about this work of the Lawless One in the churches, as seen in his first letter (2:18-19, 4:1-3) and in his second letter (v.7-11).
Although already working in the world, the full manifestation of the Lawless One is impeded by "He who now restrains" (v.6-7). There is a difference of opinion among Christian teachers with respect to the meaning of this phrase. Paul says that believers in Thessalonica already knew its meaning (v.6); therefore some commentators think that the reference is to the Roman Empire; others think it means human government while it has its existing authority (Romans 12:1-2); still others are of the opinion that "He who now restrains” refers to the Holy Spirit, Who will cease to oppose the full manifestation of Lawless One after the rapture of the Church.
In any case, Christians know that the Lawless One will be "destroyed" when the Lord comes in glory (v. 8). In Revelation 19:20 we read that the Beast and the "false prophet" will be cast alive into the Lake of Fire, which is the "second death" (Revelation 20:14).
Despite this sad prophecy concerning the fate of wrong and untrue Christianity, the apostle can thank God for the salvation of true believers (like those in Thessalonica), who, having believed in the Truth (the Gospel of the apostles) were sanctified by the Holy Spirit to reach the glory of the Lord Jesus Christ. See Romans 8:28-30.
In view of this election and sanctification, believers should stand firm, maintaining and following the true teachings of the apostles. Today we have these teachings in the New Testament letters, the book of Acts and Revelation - all of which, together with the four gospels and the books of the Old Testament, form the Holy Scriptures - the one true Word of God to the world.
Two great blessings (among many more!) are received by believers through the love of God revealed in the Gospel: we have everlasting consolation and good hope (v. 16-17) and the apostle wishes them for his readers so that the reality of their faith may produce its fruit both in conversation and in works.
1 N ow, brethren, concerning the coming of our Lord Jesus Christ and our gathering together to Him, we ask you,
2 not to be soon shaken in mind or troubled, either by spirit or by word or by letter, as if from us, as though the day of Christ had come.
3 Let no one deceive you by any means; for that Day will not come unless the falling away comes first, and the man of sin is revealed, the son of perdition,
4 who opposes and exalts himself above all that is called God or that is worshiped, so that he sits as God in the temple of God, showing himself that he is God.
5 Do you not remember that when I was still with you I told you these things?
6 And now you know what is restraining, that he may be revealed in his own time.
7 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.
8 And then the lawless one will be revealed, whom the Lord will consume with the breath of His mouth and destroy with the brightness of His coming.
9 The coming of the lawless one is according to the working of Satan, with all power, signs, and lying wonders,
10 and with all unrighteous deception among those who perish, because they did not receive the love of the truth, that they might be saved.
11 And for this reason God will send them strong delusion, that they should believe the lie,
12 that they all may be condemned who did not believe the truth but had pleasure in unrighteousness.
13 But we are bound to give thanks to God always for you, brethren beloved by the Lord, because God from the beginning chose you for salvation through sanctification by the Spirit and belief in the truth,
14 to which He called you by our gospel, for the obtaining of the glory of our Lord Jesus Christ.
15 Therefore, brethren, stand fast and hold the traditions which you were taught, whether by word or our epistle.
16 Now may our Lord Jesus Christ Himself, and our God and Father, who has loved us and given us everlasting consolation and good hope by grace,
17 comfort your hearts and establish you in every good word and work.
2 Thessalonians chapter 2