Paul gives what appear to be very clear instructions about when the anti-christ would appear.
2Th 2:1 ESV Now concerning the coming of our Lord Jesus Christ and our being gathered together to him, we ask you, brothers,
The topic Paul is discussing is ‘the coming of our Lord Jesus Christ and our being gathered to him’. This is most likely a reference to the rapture of the church which Paul had already talked about in his previous letter to the Thessalonians. He uses the same phrase ‘the coming of the Lord’ in that passage.
1Th 4:15-17 ESV For this we declare to you by a word from the Lord, that we who are alive, who are left until the coming of the Lord, will not precede those who have fallen asleep. 16 For the Lord himself will descend from heaven with a cry of command, with the voice of an archangel, and with the sound of the trumpet of God. And the dead in Christ will rise first. 17 Then we who are alive, who are left, will be caught up together with them in the clouds to meet the Lord in the air, and so we will always be with the Lord.
However it appears that some people had been creating problems in the church by saying that the rapture which Paul spoke about had already taken place and that they had been left behind. So Paul says:
2Th 2:2 ESV we ask you, brothers, not to be quickly shaken in mind or alarmed, either by a spirit or a spoken word, or a letter seeming to be from us, to the effect that the day of the Lord has come.
He continues to warn against people who are trying to deceive them. To aid against this deception, he explains what must precede the ‘coming of the Lord and our being gathered to him’.
2Th 2:3 ESV Let no one deceive you in any way. For that day will not come, unless the rebellion comes first, and the man of lawlessness is revealed, the son of destruction,
We are here introduced to the ‘man of lawlessness’, another name for the anti-christ. He is the key sign the believers should be looking for. Paul says the day when we are gathered to him will come after, not before, the anti-Christ is revealed. So, if the anti-christ is not yet revealed then believers can be certain that the day when the Lord comes for His people has not come.
Paul then describes in more detail what the anti-christ will do in order to help believers identify who he is.
2Th 2:4 ESV 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.
Finally, he chides the church for not remembering this simple truth. He had already taught them this and so there is no reason they should be anxious about having missed the coming of the Lord and their being gathering to him. Why? Because the anti-christ is not yet revealed.
2Th 2:5 ESV Do you not remember that when I was still with you I told you these things?