Philip Schaff, the great nineteenth century historian, on the error of identifying Rome with the Church Catholic:

[Rome’s] hierarchy is an absolute spiritual monarchy culminating in the Bishop of Rome, who pretends to be nothing less than the infallible Vicar of Jesus Christ on earth. It proudly identifies itself with the whole Church of Christ, and treats all other Christians as schismatics and heretics, who are outside of the pale of ordinary salvation.

But this unproved assumption is the fundamental error of the system. There is a vast difference between Catholicism and Romanism. The former embraces all Christians, whether Roman, Greek, or Protestant; the latter is in its very name local, sectarian, and exclusive. The holy Catholic Church is an article of faith; the Roman Church is not even named in the ancient creeds. Catholicism extends through all Christian centuries; Romanism proper dates from the Council of Trent.

The Creeds of Christendom, vol. 1, pp83f