I generally avoid this subject because there is much unadulterated bullshit about it. Here is an excerpt from my updated notes on 2 Thessalonians 2.
Now we come to the point of this second letter to Thessalonica. Someone was trying to convince the church there that the Day of the Lord had come, as if that would explain their persecution. Paul warned them not to believe any such notion, whether it comes via spiritual revelation, a report of teaching or a bogus letter from Paul himself. During those three short weeks with them, he warned them that there would have to be certain conditions fulfilled before the Lord’s Return.
Paul runs through a brief summary of what he had previously taught them in more detail, which detail is no longer available to us. However, the outline is not hard to follow. First, there must be a general apostasy, but it is paired directly with the rise of an Antichrist figure claiming to be Christ. This draws a picture of the church drifting far, so very far that it mistakes some satanic deceiver for Christ. In other words, the genuine Return of Christ would be preceded by a fake one. This someone will eventually claim to be God. In his previous letter, Paul draws a picture of Christ coming in the air, and then we rise to meet Him. He changes and redeems all Creation, and then comes Eternity in Paradise. Christ will not return to stand on this world in its current fallen state. The qualitative difference is indescribable, so anything short of that means Christ has not come. Signs and miracles are not evidence of any new revelation from God that contradicts plain teaching and Scripture.
You can read the rest here at the Kiln of the Soul blog.