Christ instituted the Papacy when he said to Peter that upon this rock he would build His Church (Matthew 16:18). Now, on this passage rests the conclusion that the Church's authority, through Peter, is passed down to his successors, known as the Bishop of Rome.
This is basis of the Catholic principle that this Church, this citadel, this fortress, known as the Catholic Church, is under the authority of the Pope, and history backs this up.
The Catholic Church's critics, Protestants and Catholics alike have ignored this information; or, those that know it have sequestered it; and many other critics do not even know of it.
For instance, not much is known about the early Church, and even less records survived. But what did survive are certain facts and a letter. The facts are that St. Peter, sometime between A.D. 64 and 67 was martyred in Rome, Italy (most authorities consider 67 was his martyr date). However, before his martydom, he trained for the priesthood two men, Linus and Clement I.
Linus succeeded St. Peter as Bishop of Rome (Pope). Very little is known of this man, except that he was ordained a priest by St. Peter, and had helped give solace to Saint Paul in his last lonely days.
The interesting thing about this man, Linus, is that during his time, St. John of the Apocalypse (the evangelist) had legal right to the Papacy--he was still living in Ephesus (now known as Turkey), but he turned it down. He could have claimed it and no one would have contradicted him; but he did not want it. He was busy doing other things.
Therefore, Linus became Bishop of Rome or the head of the Catholic Church, simply known as the Church at that time. He served as head of the Church for about ten years. He was succeeded by another man about whom even less is known, Cletus.
The next Pope or Bishop of Rome was Clement I. He knew St. Peter, as Linus, personally. He was trained for the priesthood by St. Peter and ordained by him. Clement I was the fourth Pope of the early Church and was in all probability a former slave. He became head of the Church at/or about A.D. 92 and died probably in 101. What he did as Bishop of Rome, we know almost nothing.
Still, during this time, St. John the Evangelist was still alive...he was getting quite old; but he still could have claimed the Papacy, he did not. He was busy writing the Apocalypse.
However, history has a letter from this period of Pope Clement I, the one great thing that survived in toto from the early Chuch. It has been read by thousands of theologians, Catholics and Protestants, and others. They all agree, it is authentiic. In it, he points out, Peter's martrydom as a fact known to all Christians.... He and Linus were both ordained by Peter. The implication is Linus and Clement were students of the priesthood under Peter.
This letter is of historical significance. It shows the Papacy was instituted by God, Jesus Christ, second person of the Holy Trinity. It illustrates the succession of the Popes from St. Peter as the heads of the Church and are to maintain authority over the Church.
This letter was written to the Church of Corinth to its Christians who were having schisms and divisions in the early Church. Clement sent this letter to the early Church to quiet the divisions and arguments. In it he explained the "doctrine of apostolic succession" This is what he wrote:
The apostles preached the gospel to us from the Lord Jesus Christ. Christ, therefore, is from God, and the apostles are from Christ.... As they preached, therefore, in the countryside and in the cities, they appointed their first fruits--after having tested them through the Spirit--to be bishops and deacons of the future believers.
He went on and cautioned strongly the Corinthians against having disputes and factions in the Church and hell-raising among themselves. He ends this warning by saying:
If some shall disobey the words which have been spoken by Him through us [Clement] let them know they will involve themselves in no small transgression and danger.
What he just said here is the Bishop of Rome--The Pope--has authorithy, given by God, over the Church in Corinth, such that disobedience to the Pope in Church matters is disobedience to God and this is SIN, because God instituted the Papacy and its line of succession.
This letter was read and preserved by the Church of Corinth for over three-hundred years on Sundays as proof of the acceptance of this letter from Clement I in the early Church.
The Catholic Church has the original text of the letter as preserved from the Church of Corinth. Many legends have sprung up around Pope Clement I, but this letter is no legend. It is factual piece of history. It shows that the "Keys of This Blood" are the keys that Christ had given to the successors of the Bishops of Rome.