Someone had started the rumor that Jesus had returned and taken his children with him. Some of the Thessalonians had believed the rumor and were frightened that they had missed the Lord's return. Paul writes about specific things that must happen before The Lord gathers his children to himself and that those things had not yet taken place.
Paul said, "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, 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" (2 Thessalonians 2:1-4).
Yet scripture also tells us to be continually ready for Christ's return (Matthew 24:24). How do these two pieces of the puzzle fit together? We do not yet know who is the Anti-Christ so why should we be ready at all times. Won't there be time to get ready after we know who the Anti-Christ is?
No there won't, because, as Paul makes it clear, when the Anti-Christ is revealed he will perform signs and wonders (miracles if you will) that will deceive those who are not obeying God before the Anti-Christ appears (2 Thessalonians 2:8-10).
The time to be ready is now.
