The epistle of Second Thessalonians was written to dispel a delusion brought in by false teachers confounding the coming of the Lord with His day, and to show that the persecutions they were enduring were not in any way "the Day of the Lord."

It is now that the faithful are called to suffer as a privilege, but the Day of the Lord will be precisely the time when there will be no more persecution for the people of God. In fact, that Day will display two facts—the saints of God in perfect rest and joy and blessedness with Christ, and their enemies under retributive dealings from God who will lay His hand heavily upon them bringing death and destruction.

The object of the Day of the Lord is not the saints at all, but to judge the evil that is in the world, the lawlessness which is already at work secretly, and which is going to result in the most open and appalling opposition to God. In short, the Day of the Lord cannot come until there is the falling away or the apostasy, and the man of sin is revealed. The reason for this is very simple. The Day of the Lord supposes divine judgment executed on an evil state of things on earth. When that development has reached its height, then the Day of the Lord will come upon it with the Lord Himself the executor of that judgment upon the earth, the nations and their inhabitants.

The Day of the Lord always involves two things—manifestation and judgment. In the full sense it is that particular phase of His presence in which He deals with what is opposed to God, and displays Himself righteously before man.

—Adapted from The Coming and Day of the Lord by W. Kelly