Francis Turretin on why the Church of Rome is not a true Church of Christ:
7. Because Antichrist sits in her.
XXI. Seventh, Antichrist sits in her, the author of the great apostasy described by the apostle in 2 Thess. 2 who, under the pretext of a vicar, professing himself be in the place of Christ (anti christou), by impiously usurping the authority of the Lord betrays himself to be really Antichrist (antichriston), the rival of him and an opposing and self-exalting enemy (antikeimenon, kai, hyperairomenon) who, sitting in the temple of God as if he were God, exalts himself above all that is called God (to wit, emperors, kings and princes of the earth, and departed saints in heaven) and shows himself that he is God. That all these criteria of Antichrist can be found in the Roman pope can easily be gathered from a comparison of both, as has been proved at length in our Disputation 7, “De Necessaria Secessione,” Opera (1848), 4:147-77.
8. Because she is Babylon.
XXII. Eighth, she is the mystical Babylon, from which the pious are commanded to come out (Rev. 18:4) as a most corrupt society diametrically opposed to the mystical Zion, the true church of Christ, and incompatible (asystatos) with it. Both the description of John proves and our opponents themselves do not deny that by Babylon is meant no other than Rome. John’s description (Rev. 17) belongs exactly to her alone, especially as to the two marks by which he distinguishes her: that she is a seven-hilled (eptalophos) city, who “sitteth on seven mountains” (v. 9); and that she obtains power over the kings of the earth (v. 10). It is evident that she is seven-hilled and in the time of John no other except herself was the mistress of the world, the head of the earth and the queen of nations, who on this account was called by the Greeks “the ruling city” (basileuousa polis).
–– Francis Turretin, “Institutes of Elenctic Theology” Vol. 3, p, 133