This question is answered in the first 12 minutes of this panel discussion at this year’s Ligonier National Conference (April 12, 2025):

https://www.youtube.com/embed/fLctU-4vzX0?si=495h4YVcVyzabz9b

Transcript: (slightly modified for clarity)

Chris Larson:  In classical Reformed theology, what is the most historically orthodox and accepted interpretation of Matthew 16:18? And I tell you, you are Peter, and on this rock, I will build my church and the gates of hell shall not prevail against it.

Dr. W. Robert Godfrey: Well, I think the two dominant Protestant approaches to that is that the Rock is Christ, which is always a good place to start.

Peter in his first epistle says, the rock of the church is Christ. So, if Peter is central in Matthew 16, we ought to listen to Peter. Peter says, the rock is Christ.

Others have said that the rock on which the church will be built is the confession of Peter, confessing that Jesus is the Christ.

The name Peter and the word for rock and Greek are related, but they’re not identical, which I think does point that it’s not really Peter on which the church is built, but it’s Peter’s confession or Peter’s Messiah on which the church is built.

Dr. Derek Thomas: Sinclair, do you agree with that? Come on. I know you don’t.

Dr. W. Robert Godfrey: It’s all right.

Dr. Sinclair Ferguson: Not being a church historian, you can’t a hundred percent trust my judgment on this, but I think that this issue did not become controversial until the Bishop of Rome was claiming authority over the whole church, and the supremacy of the church in Rome. And until that point there was a variety of views of how you interpret it (Matthew 16:18). And at least from my limited knowledge of the history of the reformed tradition, those various views have continued, so in a sense to ask what is the orthodox reformed view, looking for a narrow answer is actually to ask a question that the history of the reformed tradition does not itself answer. My personal view is nearer the second view that, that Bob mentioned. I think that actually, that is a specific prophecy about how Christ is going to build the church. That Paul indicates that the church is built on the foundation of the apostles and prophets Christ Jesus himself being the chief cornerstone.

And I think if you hold together everything that’s in that statement… I think you, you have there the nuance … the lenses through which you should interpret Matthew 16:18. Because as a matter of fact, while the keys are given to all the apostles, it is Peter who first of all takes them out of his pocket and opens the kingdom. Which is what Matthew 16:18 to 20 is really about.

It’s Peter who then opens the door of the church to the Gentiles again through the preaching of the gospel. So, I think there is in Matthew 16:18, not just a general statement about, I’m going to build my church. But I am going to use these particular individuals of whom Peter seems to be a key and I think it is significant as I think I maybe said the other day, that every time the apostles are listed, whether it’s all 12 of them or whether it’s just three of them, Peter is always the first name.

And that should be no more difficult for us as Protestants than the role we understand that is given to the Apostle Paul to be the apostle to the Gentiles. And I think it’s partly because of the controversy that has surrounded Matthew 16:18, that we Protestants are far more comfortable about speaking about the Apostle Paul as the great apostle. He is our apostle, and we are very nervous about thinking that Christ might have given a role to Simon Peter.

And then I think we can understand this because I think one of the things we see, we see this among ourselves that Christ has called us to a common ministry, but he’s given each of us different roles. And if it were not for the Roman controversy, I think we would be comfortable about seeing that Jesus is speaking to Peter in particular not abstracted either from all of the other apostles, nor abstracted from the fact that Peter is confessing Christ. But that within that context, Peter did have a rather singular role that was given to him in the church.

Dr. W. Robert Godfrey: Yeah, I think that’s absolutely true and, and I think it is important, maybe this is a crucial question for next year. But, I think it’s very important, even if we all agreed that Peter himself individually is the rock on which the church is built, even if we granted that in terms of the exegesis of Matthew 16, it does not in any necessary way imply that the Bishop of Rome continues the work of Peter. So that kind of move by our Roman Catholic friends, doesn’t necessarily follow. And when you look at the history of the church, the Bishop of Rome doesn’t really even claim Petrine authority until the middle of the third century. And now I know what you’re all thinking. You’re all thinking, why haven’t I mentioned Canon three of the Council of Constantinople.

Dr. Sinclair Ferguson: Yeah. Why haven’t you mentioned the Third Cannon of the Council of Constantinople?

Dr. W. Robert Godfrey: Well, I didn’t want to confuse you. It’s very interesting because the meeting of the Council of Constantinople is held in Constantinople. It’s the kind of useful things church historians can tell you. And at the council, they adopted the third cannon, which says, the Bishop of Constantinople has primacy of honor in the church after the Bishop of Rome because Constantinople is the new Rome. And the Pope was furious. This is 381. The Pope was furious because the council had in effect declared the Bishop of Rome has honor only because he’s bishop in the old capital of the empire, not because he’s the successor of Peter. And so the Bishop of Rome refused to acknowledge Canon three of the ecumenical council.

So it’s very interesting the church as a whole gathered in an ecumenical council, says something about the Bishop of Rome and the Bishop of Rome rejects it. So, this notion that the voice of the ancient church is unified in declaring, the role of the Bishop of Rome is simply untrue.

Is that profoundly helpful?

Dr. Sinclair Ferguson: Well, it’s funny. Yeah.

Dr. W. Robert Godfrey: That’s all I’m here for.

Dr. Sinclair Ferguson: I think it’s interesting just by way of confession. When I was a young teenager seeker, I saw an advert for 21 lessons about the Christian faith, and I sent off for them. And they came to me in a brown envelope, and I realized they’d come from the Catholic Truth Society. So in the interest of full disclosure, my name may be somewhere down in the dungeons of the Vatican as somebody to just keep your eye on. [laughter]

But even as a teenager, I noticed in all of these 21 lessons, I used to get up early on Tuesday and Thursday morning. Because I was frightened my mom and dad would discover what was happening. But even as a teenager, I noticed that they would have some Bible material and then the transition would be, “and is it not reasonable to think?” And I used to think as a dark-minded Scottish boy, I don’t actually see that as being reasonable because it doesn’t grow out of the passages that you’ve indicated to me.

And then later on I realized that the arguments that were used for the papacy were always extra biblical arguments. Isn’t it reasonable to assume that since we are in the empire and there needs to be a succession plan that’s so in the church there also should be a succession plan? And I think it dawned on me then that actually the big difference between Roman Catholics and Protestants at ground level is, we believe that God has spoken exclusively in His word, and the Roman Catholic believes that there are two strands of revelation. One is God’s word and the other is the strand of sacred tradition. And inevitably, when you have a second strand of revelation, the second strand trumps the first strand. That statement is no political reference, by the way. That’s true of the charismatic movement, and by and large, it’s true of Roman Catholics. Even the Roman Catholic leaders who have expressed in places very fine biblical theology will then add, “and here is what the church believes.” And that is a radical distinction between ourselves and Rome. And I’m just agreeing with the third canon of the Council of Constantinople, with which we are all now familiar. [laughter]

Dr. W. Robert Godfrey: What a good man! What a good man! It also is true, very briefly, that we don’t need a succession plan for the head of the church. Because we have a king who never dies.

Transcript from a Conference Question and Answer Session with Dr. R. C. Sproul – Pittsburgh, 2000

Questioner to Dr. R. C. Sproul: “How do you feel about the Vatican and its doctrine? Can you believe in this and still be saved?”

R.C. Sproul: “If they are asking, ‘Can you be a member of the Roman Catholic Church and be saved?’ I would say, ‘Without question, Yes!’ If you understand fully the doctrines of the Vatican and embrace them, then I would say, ‘No, you can’t.’

That’s because to embrace the teaching of Rome, clearly understood, you would have to repudiate the gospel – particularly the doctrine of justification by faith alone, which contrary to the press releases of the accord with the Lutherans and all of that, the Roman Catholic Church has not changed its teaching from the Council of Trent one bit. The Council of Trent (the middle of the 16th Century) was where they set forth their condemnation of the Reformation view of justification and set forth the expression of their own doctrine of justification.

Questioner: “Which is?”

R.C. Sproul: “Well, its complicated, but real quickly, the doctrine of justification in Rome involves several elements. It begins with baptism (sacramentally) where in the sacrament of baptism, justifying grace is infused into the soul of the recipient (its called the righteousness of Christ). It is infused ex opere operato (through the working of the sacrament). That infusion of grace places the infant in a state of grace and two things have to happen: one, they must cooperate with that grace and assent to that grace to be justified, (‘coopere et assentara’ are the exact words of Trent) to such a point that righteousness inheres in the soul for them to be saved. Now as long as righteousness inheres in the soul, you are in a state of justification (you are in a state of grace) until or unless you commit mortal sin. Mortal sin is called mortal sin because it kills the grace of justification in your soul. Now here’s also what is spelled out at Trent – you can commit mortal sin while you still have authentic faith – so you can have faith and not have justification – so faith alone will never suffice.

Faith is determined at Trent to be the fundamentum (the foundation), the initium (the initiation), and the rodex (the root of justification) – so you’ve got to have faith, but faith alone will not do it.

Now if you commit mortal sin, you don’t get re-baptized, even though you have lost the grace of justification, you go to the second plank of justification which is the sacrament of penance, defined by Trent as the sacrament for those who have made shipwreck of their souls. In the sacrament of penance you have to make confession, you have to get priestly absolution, and then you have to do your works of satisfaction which are necessary to gain meritum de congruo (or congruous merit) – merit that does not oblige God to redeem you but makes it fitting for God to restore you to a state of grace. And as long as you stay then in that state of grace and you have inherent righteousness (righteousness that is in you) then you will be saved. But if you die with any impurity on your soul, you go to purgatory (the purging place) until the impurity is removed.

The Protestant and I believe biblical view is that the moment you put your faith and trust in Jesus Christ, all that He is and all that He has – becomes yours in the sight of God. And that the righteousness by which we are justified is not our inherent righteousness but strictly and solely the righteousness that Luther said is extra nos (outside of us) a iustisium alienum (an alien righteousness), somebody else’s righteousness. That’s the gospel – that what saves me is not my inherent righteousness but the righteousness of Christ that was performed in His life. Not in my life, in His life. And the moment I put my faith and trust in Him, I am redeemed forever.

I don’t have to worry about purgatory, I don’t have to worry about works of congruous merit, I don’t have to worry about inherent righteousness – I mean God is going to make me inherently righteous in heaven, but my justification does not rely upon that. It is not the gospel to go tell people, here, the grace of God will help you become inherently righteous, why don’t you come and join our church and we will give you the sacrament of grace to help you. That’s not the gospel.”

Article by ​Leonardo De Chirico, pastor of the Church Breccia di Roma: