Updated: May 15, 2021
By Luke Lancaster
Catholics have been pointing to Matthew 16 for eons to prove the papacy. This has been the case because, if Christ gave the keys of His Kingdom to Peter, then that would indicate Peter to have a high ranking position in the Church. Now, the understanding of the Old Testament background of the keys seems to have hit a high point in the 1500's.
During the 16th century, many Catholics were responding to Martin Luther and his popular teaching that the Pope's authority was non-existent. These Catholics pointed out how, for Peter to hold the keys would be akin to making him governor of Christ's Kingdom here on earth. For in the Old Testament, to hold the "keys" would mean that you held the privileged position of the Prime Minister. This could be seen most clearly in Isaiah 22:22, where the Prime Minister Eliakim held the keys to King Hezekiah's Kingdom of Israel. Let's see how interpreters from the 1500's connected Isaiah 22 and Matthew 16 to refute the followers of Luther.
Cardinal Cajetan. He was sent to respond to the stir that Luther was causing in Germany, and said in 1521 that the Pope had authority because he was the possessor of Christ's keys. These "keys" Christ mentions giving to Peter were referencing the lines of Isaiah 22:22, where Eliakim held the keys to the Davidic Kingdom. See the book, Cajetan Responds: a reader in Reformation Controversy (Catholic University of America Press, 1978, edited and trans. Jered Wicks, p. 115).
St. Francis de Sales. He was sent to the Calvinists in France to attempt to bring the followers of Luther back into the Catholic Church. He had great success, converting as many as 30-70k people! One of the main ways he did this was through pamphlets he wrote, which were later collected and compiled into a book. He wrote about the papacy in one of his tracts, and emphasized that Christ gave the keys of His Kingdom on earth to Peter, which was putting him in the position of Prime Minister like Eliakim in Isaiah 22:22. See the book, The Catholic Controvery (TAN publishers, 1989, trans. Henry Mackey, pgs. 254-255).
Cornelius Lapide. Cornelius was a Jesuit Scripture scholar that wrote extensive commentaries on the Sacred Page. A contemporary of St. Robert Bellarmine, Cornelius was very interested in converting the followers of Luther back into Christ's Church. So, when commenting on Matthew 16, Cornelius connects the keys of the Kingdom with Isaiah 22:22, indicating that Christ had the position of Prime Minister in mind. See the book, The Great Commentary of Cornelius Lapide (John Hodges publishing, 1893, trans. Thomas Mossman, 4th edition, Volume 2, p. 225).
As we have seen, this interpretation of Matthew 16 being a reference to Isaiah 22 has a solid tradition behind it. Most biblical scholars today believe Jesus was referring to Isaiah 22 when giving Peter the keys, and some like to claim that this is a totally new interpretation. But as we have seen, they are not pointing out something new. Catholicism has used this powerful argument to support the papacy for at least the last 500 years, so let's never forget it!