The online New American Bible introduction to Second Thessalonians acknowledges: "Increasingly in recent times, however, the opinion has been advanced that 2 Thessalonians is a pseudepigraph, that is, a letter written authoritatively in Paul's name, to maintain apostolic traditions in a later period, perhaps during the last two decades of the first century. [my emphasis]" Mary Ann Getty-Sullivan, The Quick Reference Guide to the Catholic Bible (online), agrees, saying the author's style imitates Paul's and even copies phrases of 1 Thessalonians. This is, in fact, the majority view among biblical scholars. Burton L. Mack says in Who Wrote the New Testament, page 112, that 2 Thessalonians lacks the personal warmth, reminiscences and references characteristic of the authentic letters of Paul. Almost one-third of it is a verbatim copy from the first letter, the signature is suspicious, and the eschatology reflects a development of Christian apocalyptic thinking of the kind that took place only after the Roman-Jewish War around the turn of the first century.
Second Thessalonians can be read as a response to Paul' First Letter to the Thessalonians. Paul thought the coming of Jesus was imminent and had told the Thessalonians that this would happen in his own lifetime, as is especially clear in 1 Thessalonians 4:17: “
the dead in Christ will rise first; then we who are alive, who remain, will be caught up together with them to meet the Lord in the air.” In 1 Thessalonians, the end will come like a "
thief in the night," with Jesus appearing when people least expect it.
Decades later, and after the death of Paul, Jesus had not yet returned. The author of 2 Thessalonians argues that the end is not coming right away, and because certain things have to happen first, they will know when Jesus is coming.
2 Thessalonians 2:1-2 says that regarding the coming of the Lord Jesus Christ, a false letters written in Paul’s name had said that the day of the Lord is at hand - an apparent reference to First Thessalonians, asking that the Thessalonians not be deceived. First there must be some signs, including the appearance of the antiChrist, "the one doomed to perdition."
If 2 Thessalonians 2:2 is really a reference to 1 Thessalonians, as it appears, then both epistles can not be genuine - either 1 Thessalonians is false or 2 Thessalonians is, and we know the majority of biblical scholars say that 2 Thessalonians was not really written by Paul (regardless of whether verse 2:2 is referring to 1 Thessalonians). The (2 Thess 2:3) apostasy will not happen and “lawless one”, the anti-Christ, will not appear.