In response to your quote,"Catholics were the original Christians,"
Protestants were Roman Catholic until the Roman Catholics decided (by virtue of the Magisterium) to change their doctrine in ways that the Protestant factions within the Church could not accept.
Doctrines such as Indulgences, Mary as Mediatrix and advocate, the Praying of the Rosary, and the Doctrine of Pergatory WERE NOT PART OF THE EARLY ROMAN CATHOLIC CHURCH. These doctrines were added by various Popes and councils over the history of the Roman Catholic Church, and with the institution of the Doctrine of Papal infallibility (also NOT part of the beginnings of the Church) cannot be changed (because to do so would admit that Papal doctrine is not infallible).
Therefore, Protestants were part of the early Life of the Roman Catholic Church until their conciences could not accept the gradual additions made to the Church through the Magisterium.
In fact, the Anglican communion, though NOT in communion with the Roman Catholic Church, still recites the Nicene Creed in the Eucharist, each member proclaiming that, "I believe in one holy catholic Church." Anglicans use the word catholic to mean "universal," as in "the one body of Christ," even though Roman Catholics proclaim that THEY are the ones who are Catholic, note the capital "C".
Roman Catholics seem to be in a corner, because the Bible says that no one is sinless but Jesus Christ himself. The Roman Catholics say that the Pope's doctrines are "infallible," i.e. always right, i.e., perfect and divinely inspired. Roman Catholics also call the Pope "Holy Father." The Bible says that no one should be called Father except our Father in Heaven. I am beginning to see a problem here. Roman Catholics call their Pope "Vicar of Christ." The meaning of the word Vicar is "substitute", or "replacement." Therefore, Roman Catholics call the Pope, "Substitute of Christ on earth," or "Replacement of Christ on earth." The Bible says that ," Thou shalt have no other gods before me." The Bible also says," There is only one savior, Jesus Christ our Lord." Therefore, no human can replace Him! Roman Catholic doctrine differs from the truth of the Bible, as you have just read. This is the problem that caused so many denominations to splinter off from the Roman Catholic Church. Each denomination has the mission to express faith in Jesus Christ our Lord, and to obtain forgiveness for our sins and to amend our lives so that we may be conformed to the likeness of Christ, and to have hope in the world to come through the hope of the ressurection of Christ, although each denomination certainly has different ways of going about trying to accomplish this goal!
I hope this clears things up for you.
Jesus is Lord!