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Interpretation of Matthew 16:18

To better understand what Christ meant, St. Basil elaborates:

Though Peter be a rock, yet he is not a rock as Christ is. For Christ is the true unmoveable rock of himself, Peter is unmoveable by Christ the rock. For Jesus doth communicate and impart his dignities, not voiding himself of them, but holding them to himself, bestoweth them also upon others. He is the light, and yet you are the light: he is the Priest, and yet he maketh Priests: he is the rock, and he made a rock.

In reference to Peter's occupation before becoming an Apostle, the popes wear the Fisherman's Ring, which bears an image of the saint casting his nets from a fishing boat. The keys used as a symbol of the pope's authority refer to the "keys of the kingdom of Heaven" promised to Peter. The terminology of this "commission" of Peter is unmistakably parallel to the commissioning of Eliakim ben Hilkiah in Isaiah 22:15–23. Peter is often depicted in both Western and Eastern Christian art holding a key or a set of keys.

In the original Greek the word translated as "Peter" is Πέτρος (Petros) and that translated as "rock" is πέτρα (petra), two words that, while not identical, give an impression of one of many times when Jesus used a play on words. Furthermore, since Jesus presumably spoke to Peter in their native Aramaic language, he would have used kepha in both instances. The Peshitta Text and the Old Syriac texts use the word "kepha" for both "Peter" and "rock" in Matthew 16:18. John 1:42 says Jesus called Simon "Cephas", as Paul calls him in some letters. He was instructed by Christ to strengthen his brethren, i.e., the apostles. Peter also had a leadership role in the early Christian church at Jerusalem according to The Acts of the Apostles chapters 1–2, 10–11, and 15.

Early Catholic Latin and Greek writers (such as St. John Chrysostom) considered the "foundation rock" as applying to both Peter personally and his confession of faith (or the faith of his confession) symbolically, as well as seeing Christ's promise to apply more generally to his twelve apostles and the Church at large. This "double meaning" interpretation is present in the current Catechism of the Catholic Church.

Protestant arguments against the Catholic interpretation are largely based on the difference between the Greek words translated "Rock" in the Matthean passage. They often claim that in classical Attic Greek petros (masculine) generally meant "pebble", while petra (feminine) meant "boulder" or "cliff", and accordingly, taking Peter's name to mean "pebble", they argue that the "rock" in question cannot have been Peter, but something else, either Jesus himself, or the faith in Jesus that Peter had just professed. These popular-level writings are disputed in similar popular-level Catholic writings.

The New Testament was written in Koiné Greek, not Attic Greek, and some authorities say no significant difference existed between the meanings of petros and petra. So far from meaning a pebble was the word petros that Apollonius Rhodius, a writer of Koiné Greek of the third century B.C., used it to refer to "a huge round boulder, a terrible quoit of Ares Enyalius; four stalwart youths could not have raised it from the ground even a little".

The feminine noun petra (πέτρα in Greek), translated as rock in the phrase "on this rock I will build my church", is also used at 1 Cor. 10:4 in describing Jesus Christ, which reads: "They all ate the same spiritual food and drank the same spiritual drink; for they drank from the spiritual rock that accompanied them, and that rock was Christ."

Although Matthew 16 is used as a primary proof-text for the Catholic doctrine of Papal supremacy, some Protestant scholars say that prior to the Reformation of the 16th century, Matthew 16 was very rarely used to support papal claims, despite it being well documented as being used in the 3rd century by Stephen of Rome against Cyprian of Carriage in a "passionate disagreement" about baptism and in the 4th century by Pope Damasus as a claim to primacy as a lesson of the Arian Controversy for stricter discipline and centralised control. Their position is that most of the early and medieval Church interpreted the "rock" as being a reference either to Christ or to Peter's faith, not Peter himself. They understand Jesus' remark to have been his affirmation of Peter's testimony that Jesus was the Son of God.

Despite this claim, many Fathers saw a connection between Matthew 16:18 and the primacy of Peter and his office, such as Tertullian, writing: "The Lord said to Peter, 'On this rock I will build my Church, I have given you the keys of the kingdom of heaven whatever you shall have bound or loosed on earth will be bound or loosed in heaven'....Upon you, he says, I will build my Church; and I will give to you the keys, not to the Church."