From Corinth, Paul wrote his Second Epistle to the Christians in Thessalonica. Since he had left them, many had backslidden from his own solid and Biblical Postmillennialism.
They had lapsed into screwball Quasi-Zoroastrian Premillennialism. Indeed, they had falsely assumed that Christianity would shrink — and Jesus soon return to rapture His ‘imperilled’ Church, before the Final Judgment.
So Paul now reminded the Thessalonians that Jesus would not return physically until long after the ‘wicked one’ — Antichrist, alias ‘the man of sin’ — had later been revealed. Indeed, only thereafter would Jesus return unto Final Judgment.