When Jesus asked his disciples, “But who do you say that I am?” Simon answered, “You are the Christ, the Son of the living God.” Jesus replied to him,

 

Blessed are you, Simon son of Jonah, for this was not revealed to you by flesh and blood, but by my Father in heaven. And I tell you that you are Peter (Πέτρος - Petros), and on this rock (πέτρᾳ - petra) I will build my church, and the gates of Hades will not overcome it. I will give you the keys of the kingdom of heaven; whatever you bind on earth will be bound in heaven, and whatever you loose on earth will be loosed in heaven (Matthew 16:18-19).

 

Who or what is the “rock” on which Jesus says he will build his church? The answer to that question is contentious, more for theological reasons than for grammatical ones.

 

Catholics (and many Protestants) believe that Jesus was referring to Simon himself as the “rock.” But many other Protestants argue that because Matthew used different words for “Peter” and “rock” (petros vs. petra), Jesus wasn’t referring to Simon, but to himself, the big boulder, in contrast to Simon, the little rock:

 

Christ Himself is called the “chief cornerstone” (1 Peter 2:6, 7). The chief cornerstone of any building was that upon which the building was anchored. If Christ declared Himself to be the cornerstone, how could Peter be the rock upon which the church was built?¹

 

Or perhaps Jesus was referring to Peter’s confession of faith, “You are the Christ, the Son of the living God.”

 

At this point, Jesus declares that God had revealed this truth to Peter. The word for “Peter,” Petros, means “a small stone” (John 1:42). Jesus used a play on words here with petra (“on this rock”) which means “a foundation boulder,” as in Matthew 7:24, 25 when He described the rock upon which the wise man builds his house. Peter himself uses the same imagery in his first epistle: the church is built of numerous small petros, “living stones,” (1 Peter 2:5) who, like Peter, confess that Jesus is the Christ, the Son of the living God, and those confessions of faith are the bedrock of the church.²

 

Before we do a deep dive into Greek grammar, bear in mind that when this scene played out, Jesus wasn’t speaking Greek, he was speaking Aramaic. He didn’t call Simon Petros, he called him Kepha. 

 

We know that for a fact because when Jesus first met Simon, he said, 

 

“You are Simon the son of John; you shall be called Kepha³ (which is translated Petros)” (John 1:42). 

 

So, this verse tells us explicitly that Simon’s new name, Petros, is a translation into Greek of the Aramaic word Kepha. Eight other times in the Greek New Testament Simon is called Kepha instead of Petros.⁴

 

It’s important to understand the play on words Jesus was using here. If you’re old enough to remember who movie star Rock Hudson was, imagine Jesus was talking to him, and the conversation went like this:

 

“I liked your latest movie, Rock, it was funny. I see potential in you. And I tell you that you are Rock, and on this rock I will build my church.”

 

It’s a pun because Rock is the man’s name, and it’s also a word referring to a foundation. The Aramaic word Kepha worked well for that pun because it can be a man’s name, and it’s also the word for “rock.” So, Jesus said, “I tell you that you are Kepha, and on this kepha I will build my church.” Protestant theologian D.A. Carson explains:

 

[T]he the underlying Aramaic is in this case unquestionable; and most probably kepha was used in both clauses (“you are kepha” and “on this kepha”), since the word was used both for a name and for a “rock.” The Peshitta (written in Syriac, a language cognate with Aramaic) makes no distinction between the words in the two clauses. The Greek makes the distinction between petros and petra simply because it is trying to preserve the pun, and in Greek the feminine petra could not very well serve as a masculine name.⁵

 

As Carson illustrates, 40 years after Jesus said those words in Aramaic, when Matthew sat down to translate them into Greek, he had a problem. He needed to preserve the “rock-rock” pun, but the Greek word for rock, petra, is feminine. He couldn’t call his pal Simon “Petra,” because that’s a woman’s name, a name that’s still in use today.⁶ It would be like calling him Simone instead of Simon. So, Matthew changed the feminine ending (-ᾳ) to a masculine ending (-ος), thus changing petra to petros.

 

Tripping over the Petros

 

As it turns out, Petros was a preexisting word in Classical Greek, centuries before the New Testament was written, and it could mean “a small stone.” But even then, according to Lutheran theologian Oscar Cullmann, “one cannot differentiate too strictly between petra and petros; they are often used interchangeably.”⁷ Also, according to D.A. Carson, the distinction between petra and petros in Classical Greek was “largely confined to poetry.”⁸

 

None of that really matters, though, because the New Testament wasn’t written in Classical Greek, it was written in Koine (or “common”) Greek. By the time Koine Greek had developed, the word petros had fallen into disuse.⁹ In fact, according to Protestant New Testament scholar R.T. France, “petros as a common noun is unlikely to have been familiar to Matthew’s readers.”¹⁰

 

This is borne out by the fact that the word petros occurs 162 times¹¹ in the New Testament, and every single occurrence is Simon’s name. Not once is petros used as a common noun to mean a stone, or a rock, or anything else.

 

But wait, didn’t the quote above say, “Peter himself uses the same imagery in his first epistle: the church is built of numerous small petros, ‘living stones,’ (1 Peter 2:5)”?¹² Didn’t Peter himself call believers small petros? No, he didn’t. He used the word lithos, not petros. He wrote, “you also, like living stones (lithoi), are being built into a spiritual house.”

 

Lithos (λίθος) is the word commonly used in the New Testament to refer to small rocks or stones. For example, Romans 9:33 says, “See, I lay in Zion a stone (lithos) that causes people to stumble and a rock (petra) that makes them fall.” Notice that Paul uses petra here to indicate a rock that’s small enough to trip over. Petra doesn’t always mean “large boulder.”

 

What’s in a Name?

 

Another indicator that Jesus was referring to Simon as the rock is that Jesus changed his name. We’re so used to calling Simon “Peter,” that we can lose sight of the fact that in the Bible a name change was a big deal. “A name change often meant a completely altered life from the one the person had lived before.”¹³ For example, God changed Abram’s name to “Abraham,” which meant “Father of a Multitude.” He changed Jacob’s name to Israel, “because you have struggled with God and with humans and have overcome” (Genesis 32:28). And he changed Simon’s name to Peter, the rock, because “on this rock I will build my church.”

 

The Keys of the Kingdom

 

After Jesus told Simon, “You are Kepha and on this kepha I will build my church,” he added, “I will give you the keys of the kingdom of heaven; whatever you bind on earth will be bound in heaven, and whatever you loose on earth will be loosed in heaven.” (Matthew 16:19)

 

If you’re familiar with the Old Testament you might notice a parallel here between what Jesus said to Peter and what was said of Eliakim, the royal steward under King Hezekiah, in Isaiah 22:22,

 

He will be a father to those who live in Jerusalem and to the house of Judah. I will place on his shoulder the key to the house of David; what he opens no one can shut, and what he shuts no one can open.