Third. The description of the initial phases of the "man of sin" soon to be unveiled even to the A.D. 51f Thessalonian Christians — is altogether compatible with its identification as the Heathen Roman power.3927 For this power would fully be unveiled precisely after "the falling away first."
This falling away was important. For it is called "the apostasy." We are not told it would be a falling away of Christians from Christianity. Such would be impossible – for: 'once saved; always saved.' Yet it would indeed be the apostasy — somewhat like the falling away of the unsaved first-century Judaistic leaders from the Biblical and Christian teachings of the Older Testament.3928 Indeed, such in fact foreshadowed "the apostasy" which would occur later — when a papalizing Church would fall away from true Christianity (viz. from the teaching of both the Older and the Newer Testaments of the infallible Word of God).
Now the "man of sin" to be unveiled after the "taking out of the way" of Judaism as the withholding agent — would be the "son of perdition" or the great destroyer. This corresponds to Daniel's fourth or Roman Empire or Beast,3929 which would ultimately itself go into "perdition."3930 But before its own destruction, this Roman Beast would first oppose every other religion — while demanding the worship of the Heathen Roman State itself.3931
Even as Paul was writing to the Thessalonians, the Roman Beast would soon sit in the temple of God in Jerusalem and claim to be divine (as Heathen Rome did in 70 A.D.).3932 And this Roman Beast, essentially wicked, would come and make its appearance there "according to the working of Satan,3934 with all power and signs and lying wonders, and with all deceivableness of unrighteousness in them that perish — because they [who perish] did not receive the love of the truth, so that they might be saved."3935 Instead, they rather received the mark of the Roman Beast (to avoid persecution) — and so ended up by being damned.3936
Fourth. Although (in that apostolic period A.D. 4970f) Heathen Rome was obviously the beginning of this development — it was not the end of the development of "the man of sin." For it is clear3937 that pagan Rome would in
time be succeeded by Papal Rome in its place.
Either way, the 'man of sin' would keep on going into the "temple of God" alias the Church — to be seated [or enthroned] there and, cunningly, keep on claiming to represent "God" and thus to be in His place. Thus the Early Patristic Fathers; John Calvin; the Dordt Dutch Bible; and Matthew Henry etc.
So, in his Theme of the Second Epistle of Paul to the Thessalonians, Dr. John Calvin states that Paul "disproves a…fanciful belief about the imminent return of Christ…. He does so by arguing that first there must come apostasy in the Church, and a great part of the World turn from God in faithlessness. Indeed, Antichrist must reign in the temple of God."
Now never since 70 A.D. could the man of sin enter the old "fallen down" Judaistic "temple of God" in Jerusalem. But he did keep on entering into the new "fallen away" Papal "temple" later headquartered in Rome, to sit enthroned there. Too, many of the Pre-Reformers identified precisely the Papacy as Antichrist. Thus: the Waldensians; Eberhard of Salzburg; John Milicx; John Wycliffe; Walter Brute; Jan Huss; and Girolimo Savonarola.
So too all of the Reformers without exception were Protestant Historicists, who denounced the Papacy as Antichrist. Thus: Luther; the Articles of Smalcald (II:4); Melanchthon; Osiander; Flaccius Illyricus; Nigrinus; Chytraeus; Funck; Zwingli; Calvin; Bullinger; Beza; Tyndale; Knox's Geneva Bible; and Cranmer. So too: Pareus; James I; Mede; the Preamble to the Decrees of Dordt; the Dordt Dutch Bible; Thomas Goodwin; the Westminster Confession of Faith (25:6); Gerhard; Jurieu; Alsted; Turretin; John Brown of Haddington; Whitby; Sir Isaac Newton; Gill; Thomas Newton; Matthew Henry; Wesley; Bengel; Adam Clarke; Albert Barnes; James Denney; and many others.