7. The heretics, too, boast of the unity of their Churches, but St. Augustin says that it is unity against unity. "What unity," says the Saint, "can all those Churches have which are divided from the Catholic Church, which is the only true one; they are but as so many useless branches cut off from the Vine, the Catholic Church, which is always firmly rooted. This is the One Holy, True, and Catholic Church, opposing all heresies; it may be opposed, but cannot be conquered. All heresies come forth from it, like useless shoots cut off from the vine, but it still remains firmly rooted in charity, and the gates of hell shall not prevail against it" (St. Aug. lib. 1, de Symbol. ad Cath. c. 6). St. Jerome says that the very fact of the heretics forming a church apart from the Roman Church is a proof, of itself, that they are followers of error, and disciples of the devil, described by the Apostle as "giving heed to spirits of error and doctrines of devils" (1 Tim. iv. 1).
8. The Lutherans and Calvinists say, just as the Donatists did before them, that the Catholic Church preserved the true faith down to a certain period—some say to the third, some to the fourth, some to the fifth century—but that after that the true doctrine was corrupted, and the spouse of Christ became an adulteress. This supposition, however, refutes itself; for, granting that the Roman Catholic Church was the Church first founded by Christ, it could never foil, for our Saviour himself promised that the gates of hell never should prevail against it: "I say unto you that you are Peter, and on this rock I will build my Church, and the gates of hell shall not prevail against it" (Matt. xviii. 18). It being certain, then, that the Roman Catholic Church was the true one, as Gerard, one of the first ministers of Luther, admits (Gerard de Eccles. cap. 11, sec. 6) it to have been for the first five hundred years, and to have preserved the Apostolic doctrine during that period, it follows that it must always have remained so, for the spouse of Christ, as St. Cyprian says, could never become an adulteress.
