In one of the most famous scenes in Christian literature, Jesus Christ tells Simon Peter that he is the "rock" upon which the Christian church will be built (Matthew 16:18). In this verse Jesus tells "Petros" that he is the "petra" upon which the church will be constructed. We know that Peter means rock; but the gospel of John explains a pivotal aspect of this name, saying Peter is a translation of the real title given to the apostle Simon, which is Cephas. John says "Jesus said: you are Simon the son of John, thou shalt be called Cephas (which is translated Peter)" (John 1:42). And indeed the name Peter is used throughout the New Testament. But Cephas is the original title given to the head of the Christian church in the epistles of Paul. And since John was written decades later than Paul, we must examine Paul to understand the true meaning of Cephas.
In Paul's original usage of Cephas, he clearly implies “head”, not just “rock”. “Cephas” is said to derive from the Aramaic word for stone. But Cephas (Céphas) is one vowel shift away from being the same word as “head” in Greek: “cephalé”, from which we form English words like “cephalic”. Therefore Cephas is a pun in Greek at the very least, and other biblical usage demonstrates that the meanings of “head” and “stone” are closely intertwined.
Paul repeatedly compares members of the church to parts of a body, so it is not surprising that he would call the leader of the church the "head". Paul says "Just as each of us has one body with many members, and these members do not all have the same function, so in Christ we who are many form one body, and each member belongs to all the others" (Romans 12:4-5). He again describes Christians (whom he regards as a mixture of Jews and Greeks) as all parts of a single body, saying “The eye cannot say to the hand ‘I don’t need you!’ And the head [cephalé] cannot say to the feet ‘I don’t need you!’” (1 Corinthians 12:21). Paul says Jesus is the head (cephalé) of every power and authority (Colossians 2:10), and when Paul criticizes Jewish legal fanatics, he says such a person “has lost connection with the Head [cephalé], from whom the whole body, supported and held together by its ligaments and sinews, grows as God causes it to grow” (Colossians 2:19). Paul obviously favors the body as a metaphor for the church (or the church as a metaphor for the body). Therefore when he calls the head of the church a name very similar to the head of the body we should not assume he is only referring to a rock.
Paul says that Jesus Christ is the "acrogonias" that completes the foundation laid by old testament prophets (Ephesians 2:20) (see also Acts 4:10-12). The Greek prefix acro- denotes height, extremity, and sharpness, all of which may be ascribed to the head. So to speak precisely, an acrogonias is a capstone and not a cornerstone; it is the finishing touch, and not the foundation. Paul invokes an image made famous by Psalm 118:22: the capstone (or “chief cornerstone” in Hebrew) which the masons reject. Here the term “cephalén gonias” is used in the Septuagint (the Greek old testament) to mean chief cornerstone: “The stone [lithos] which the builders rejected has become the head of the corner [cephalén gonias].” This psalm actually makes a lot of sense. After all, the unique shape of a capstone makes it unfit to serve as a foundation stone. Therefore it is entirely reasonable that masons would reject such a stone at the beginning of construction, yet later use it to complete the building. Furthermore, the word “cephalén gonias” is also favored over “acrogonias” by the authors of the Gospels, changing the literal reading from high-stone to head-stone. So the authors of the Gospels take pains to emphasize the “head-stone” of prophecy while simultaneously emphasizing that the head of the church is named after a rock. Some mischief must be afoot.
The usage of “acrogonias” and “cephalén gonias” is mixed in the Septuagint as well. Isaiah famously invokes the cornerstone of Zion, and Isaiah’s writings are a central source of Christian theology. But whereas Psalm 118’s description of a capstone makes sense in Greek, Isaiah’s does not. In the Septuagint, the Lord says “Behold, I lay for the foundations of Zion a costly stone [lithos], a choice, a precious cornerstone [acrogonias] for its foundations” (Isaiah 28:16). Here the Greek translator’s choice of “acrogonias” is a poor one. As explained earlier, a capstone is no use for building a foundation. And indeed, the original Hebrew of Isaiah refers only to a corner stone; not the chief stone or “head of the corner”, but the base of the corner. Isaiah also says the Lord will lay a “stumbling stone” and “ruinous rock” (petra) that will ensnare the Israelites in Jerusalem (Isaiah 8:14). To put Isaiah in other words, the Lord will lay down a “ruinous Peter” as the foundation of Zion, and it will cause the Israelites to stumble and fall.
The first epistle of Peter actually ties these verses from Psalms and Isaiah together, saying that Jesus is both the capstone which the builders rejected and the stumbling stone that will be the foundation of Zion (1 Peter 2:7-8). Rather than Isaiah’s “ruinous petra” (“offensive stone” in Hebrew), Peter calls the stumbling stone a “scandalous petra”. But as discussed, the stone in Psalms and the stone in Isaiah have very different meanings. Only poor translation and Christianity link them together.
Furthermore, Paul does not always seem to think that Cephas and Peter are the same person. In one instance he says Christ “was seen by Cephas, then by the twelve”, implying that Cephas is not one of the twelve apostles (1 Corinthians 15:5). In another instance he mentions Peter and Cephas as if they were separate individuals (Galations 2:7-10). In fact there is no reason to think Paul is describing the same person when he talks about Cephas and Peter. Even Eusebius wrote that Cephas “happened to have the same name as Peter the apostle” (The History of the Church, Book 1, 12). This is another indication that the names do not actually have an identical meaning. Since John 1:42 offers the only reference to “Cephas” in the four Gospels, he could be pulling our leg, as he does in other matters. But why?
This brings us back to Matthew 16:18, when Jesus tells Simon Peter that he is the rock on which he will build his church. Jesus is obviously making a joke: if Simon Peter is Cephas and the “head” of the church, why is Jesus now saying Cephas will be the foundation or the foot? Paul believed Jesus was the capstone of prophecy, and Cephas was the head of the church, but Matthew says Cephas is instead the foundation of a new religion. As Psalms implies, this is impossible: no one can build a church upon a capstone, it must be saved for the finishing touch. But as the epistle of Peter elucidates, the rock referenced in Matthew may not be the scorned capstone of Psalms, but the scornful cornerstone of Isaiah. This indicates that the Gospels were written specifically to supersede the belief system of Paul: to turn the head of his church into the foundation of a new one.
A glance beyond all this literature into the actual history of the 1st century may solve the riddle. Joseph Atwill believes the Gospels are using Simon Peter/Cephas to mock the historical fate of Simon bar Giora. This Simon was born around the year 50 CE. He was later invited to Jerusalem amidst its war with Rome, where he took over the Temple and put the high priest Matthias to death. Jerusalem was not a politically unified city; various cults struggled for dominance, including the Sicarii led by Simon and the Zealots led by John. Therefore Simon bar Giora was the head of a cult in Jerusalem, the same role that Paul ascribes to Cephas. It is important to note here that this does not necessarily mean Simon bar Giora was a Christian, or even that Paul was his contemporary. It is only the Gospel of John that link Cephas and Simon together through the name “Petros”. When Titus sacked Jerusalem in 70 CE, he took Simon bar Giora back to Rome and drove him off a cliff.
Atwill shows that in War of the Jews, the Jewish historian Josephus describes Simon bar Giora as having “fled into a subterranean cavern with a bunch of stonecutters” to try to escape the Romans as they sacked Jerusalem (Caesar’s Messiah p.92). Unable to dig an escape route, Simon then “appeared out of the ground in the place where the Temple has formerly been”. Here Josephus describes Simon coming out of the ground, in other words appearing head first, at the precise location of the Temple that Titus had just destroyed. Thus Josephus implies that the head of Simon bar Giora could provide a new foundation for a new Temple. Jesus may be satirizing the fate of Simon bar Giora by saying he will build a new church upon his head.
Atwill writes, “In the Christian tradition, ‘Simon the Apostle’ suffers a martyr’s death at Rome. In fact his execution, in the manner and approximate year that the Christian tradition maintains, is described by Josephus. Simon is not, however, a Christian martyr but a Jewish one” (Caesar’s Messiah p.97). As Simon Peter tells Christ, “with you I am ready to go both to prison and death” (Luke 22:33). Likewise, the real Simon bar Giora was “kept for the Emperor’s triumph at Rome, where he was dragged through the streets and then hurled from the Tarpeian rock” (Jewish Encyclopedia).
So it appears that the New Testament regards Simon bar Giora as the ruinous rock that tripped up the Israelites and laid a foundation for Zion. He is the head/stone that became a foundation for Roman Christianity.