Paul raised the issue of the Day of the Rapture, or the Coming of Jesus for the Church. He did not bring up, initially, any sense that there was this supposed "extended day," involving the rise of Antichrist. He did bring the Antichrist up, but only to show that he must precede Christ's coming for the Church.
He did not bring this day of Christ's Coming up to indicate that people believed that the Day of the Lord was an extended period of time, or that it had already begun. He was not stating that the Departure of the Church had to take place before an extended "Day of the Lord" could begin. Since he had raised the issue up of the coming of the Lord for the Church it is that particular Day that he indicated others were declaring had already taken place. That is, others were not saying an *extended Day of the Lord* had already begun. Rather, Paul was saying that these errant brothers were claiming that the literal Day of Christ's Coming had already happened, and that the Kingdom had come in them!
When Paul compared Christ's Coming to a birth pang that comes upon a woman at childbirth, the emphasis is on the birth of the child, and not on the birth pains!
1 Thes 5.1 Now, brothers and sisters, about times and dates we do not need to write to you, 2 for you know very well that the day of the Lord will come like a thief in the night. 3 While people are saying, “Peace and safety,” destruction will come on them suddenly, as labor pains on a pregnant woman, and they will not escape.
This allegory does not denote that the Day of the Lord is a "long day," beginning with a Tribulation Period and ending with the Millennial Kingdom! Rather, it is emphasizing the suddenness of the Coming itself! A "thief" does not come with a lot of preliminary warning signs!
The birth pains in this particular passage are *immediately before* the coming of the child. They can even be said to be simultaneous with the birth of the child. And so, Paul is saying that Jesus' Coming will take place immediately, without warning, at the 1st sign of birth. There will be no warning period--no Tribulation Period to serve as advance warning. People will only see trouble in the world, just as they've always seen. And as these troubles worsen, they only curse God, and have no sense that Armageddon is about to erupt.
The Day of the Lord, therefore, begins at the Coming pf Christ for his Church, and not with the trouble that precedes it. Paul is not calling the "Day of the Lord" the "birth pains." He is not calling the "Day of the Lord" the "Tribulation Period" that precedes the coming of Christ for his Church.
In this particular scenario, Paul seems to be speaking of a woman giving birth *immediately,* at the instant birth pains show up. This is very different from the scenario in the Olivet Discourse, where Jesus describes preliminary signs indicating the fall of Jerusalem is imminent.
Before Jerusalem fell in 70 AD, there were rumors of wars and trouble brewing. There were false prophets of peace, and false proclamations of God's Kingdom entering through Israel. These were extended signs, designed to warn Jewish Christians in advance of the fall of Jerusalem.
But the birth pains Paul is describing in 1 Thes 5 are different, and have to do with the Return of Christ. There will be no advance signs to warn the world of the coming judgment at Christ's return. As soon as the birth pains begin, the child is delivered.
Isa 66.8 Who has ever heard of such things? Who has ever seen things like this? Can a country be born in a day or a nation be brought forth in a moment? Yet no sooner is Zion in labor than she gives birth to her children.
People of the world will not recognize the signs of the "Great Tribulation" period. They will not recognize the "Antichrist." They've seen many emperor and powerful kings in history. And they've seen a lot of wars and natural disasters. They will not be prepared for Christ's Coming "like a thief in the night." As soon as the birth pangs begin, the child is delivered.
No, Paul is saying that these "false conveyors" were declaring the Coming of the Lord for the Church had already come. A present indicative, as applied to the "coming," does not indicate that they believed the "day of the Lord" had already started in the past and would continue to the present. Rather, the present indicative applies to the idea that these "false conveyors" believed something in the past and still were believing it, namely that Christ had already come for his Church, and that the Kingdom was being realized in their little cult.
No, the Day of the Lord elsewhere in the Bible is applied to a variety of things, including major judgments and major blessings. But there is no singular term "Day of the Lord" that technically applies, in all cases, to all of these.
Sometimes the "day of Christ's Coming" applies only to the 24 hour day in which he returns. Sometimes it refers to the eschatological judgment of the Antichrist. At other times it refers to the initiation of the Kingdom Age. But the term "Day of the Lord" does not have one established meaning such that it must refer to all of these in each instance.
Context is king, brother! Context must determine how a word or phrase is used. And the "day" 2 Thes 2 is speaking of explicitly refers to the 24 hour day in which Christ returns for his Church--not to an extended day, including judgments and blessings that precede and follow it. You are trying to transfer a distorted idea of the "day of the Lord" in 1 Thes 5 to 2 Thes 2, but you have the meaning of the "day of the Lord" wrong in 1 Thes 5!
I believe you're misrepresenting what the Thessalonians knew and what the errant brethren were claiming, and there is nothing here in the Scriptures that claim what you are claiming. It is far more likely, from what we read, that Paul had taught the Thessalonians about the day of Christ's Coming and the "Rapture," as evidenced in 1 Thes 4. And it is much more likely that Paul did *not* define the "day of the Lord" used in 1 Thes 5 as you do, as an extended period of time, replete with pre-judgments and post-blessings.
It is far more likely that the Thessalonians had been taught what Paul, as a Jewish teacher knew, that in Dan 7 the Man of Sin would oppose God, produce a world-wide apostasy against Christ, and ultimately be destroyed at the coming of Christ 3.5 years later.
The errant brothers were teaching that somehow the Kingdom had already arrived in their cultic Christian movement, claiming authority that they didn't have. But Paul warned that their authority was feigned, and would not produce results. Instead, the Thessalonian Christians should expect continued opposition from the ungodly world until Christ himself comes back to judge the earth.
Actually Paul *is* in fact saying that these errant brothers thought the Rapture had already occurred, or at least that Christ had come to them. The Kingdom they claimed was in their cult movement, and they were somehow the Kingdom's judges and victors. Sounds a bit like Dominion Theology?