was joined by biblical interpreters of his own and of later periods; for 'the most astonishing fact' is that 'in the specifically exegetical literature of the entire Middle Ages one looks in vain for the equation "petra = Peter,"' which was so prominent in the polemical and canonical literature. [Pelikan, The Growth of Medieval Theology, p. 47; emphasis added]Just so there's no confusion: it's not that the identification of St. Peter as the rock was absent in the Middle Ages; rather, it was apparently missing from exegetical works. It's probably worth pointing out that this doesn't (and apparently didn't) have the same dispositive force for Catholics as it does for Protestants, given (among other things) the fact that Catholics have never limited themselves to the bare literal sense of the Bible.
Nevertheless this surprises me, because it seems to me that there are at least a few considerations that weigh strongly in favor of the argument that the Lord Jesus meant to identify Peter as the rock in that passage. First off, I think the parallel with Isaiah 22:22 is too strong to ignore. In that passage is described Eliakim's appointment as steward of the house of David, and what that will mean for the authority that he will possess in the kingdom; this is far too similar to what the Lord says of St. Peter in Mt. 16:19 to ignore, in my opinion. Hence St. Peter is the steward who governs Christ's household the Church in the King's absence.
A second argument involves a certain form of expression in both Mt. 16:18 and Jn. 6:51-52. Let's start with the latter, because no one quibbles about what's in view there.
I am the living bread which came down from heaven. If any man eat of this bread, he shall live for ever.Now it ought to be obvious that the subject of the first sentence ("I am the living bread") is identical with the object of man's eating in the latter sentence ("If any man eat of this bread"). Christ is the bread; whoever eats this bread (namely, Christ, the bread just mentioned) shall live forever.
Compare this with Mt. 16:18:
And I say to thee: That thou art Peter; and upon this rock I will build my church, and the gates of hell shall not prevail against it.It's the same construction as in John 6:51-52: You are Peter ("the rock"), and on this rock (namely, Peter, the one just mentioned) I will build my church. Viewed this way it seems to me to be indisputable that Peter is in view. So what about the "problem" that the gender of the two nouns is different? Well, the Lord couldn't very well call Peter by a feminine name, could he? No. He couldn't and he wouldn't. Consequently the gender difference is an accommodation. It's inconsequential. Hence it seems to me that the expressions are far similar for us to ignore the likeness: I am the bread of heaven; whoever eats this bread (namely, the bread just mentioned) shall live; You are Peter (a rock), and upon this rock (namely, the rock just mentioned) I will build my church.
I just see no grounds for argument about it. And that is why it's surprising that the schoolmen seemed not to agree. Now I'm perfectly willing to concede that given a dispute between Medieval experts and me, an armchair scribbler, there's not much likelihood that I'd be right and centuries of faithful Catholic scholars would be wrong. So I do not propose my understanding of the passage to be anything other than a hypothesis that I find persuasive. In any case, my view of the literal sense of the passage may not be consistent with how it was understood in the Middle Ages, but I think that we would certainly agree that other senses of the verse substantiate the position of Peter and his successors as the earthly head under Christ of the Church.