Paul asks the Thessalonians, concerning the coming of our Lord Jesus Christ and our being gathered to him, not to be quickly shaken in mind or alarmed, whether by a spirit, a spoken word or a letter seeming to be from the missionaries, to the effect that the day of the Lord has come. Let no one deceive them: that day will not come unless the rebellion comes first and the man of lawlessness is revealed, the son of destruction, who opposes and exalts himself against every so-called god or object of worship, so that he takes his seat in the temple of God, proclaiming himself to be God.
Paul reminds them that he already told them this. Now they know what is restraining him, so that he may be revealed in his own time. The mystery of lawlessness is already at work, but only until the one who now restrains it is out of the way. Then the lawless one will be revealed, whom the Lord Jesus will kill with the breath of his mouth and bring to nothing by the appearance of his coming. His coming is by the activity of Satan, with false signs and wonders and every wicked deception for those who are perishing, because they refused to love the truth and so be saved. Therefore God sends them a strong delusion, so that they believe what is false and are condemned.
By contrast, Paul thanks God for the Thessalonians, beloved by the Lord, because God chose them from the beginning for salvation through the sanctification of the Spirit and belief in the truth, and called them through the gospel to obtain the glory of our Lord Jesus Christ. So they must stand firm and hold to the teachings they received, by word or by letter. He closes with a prayer that the Lord Jesus and God the Father, who gave them eternal comfort and good hope, comfort their hearts and establish them in every good work and word.