Who is the rock?
Now take a closer look at the key verse: "You are Peter, and on this rock I will build my Church" (Matt. 16:18). Disputes about this passage have always been related to the meaning of the term "rock." To whom, or to what, does it refer? Since Simon’s new name of Peter itself means rock, the sentence could be rewritten as: "You are Rock and upon this rock I will build my Church." The play on words seems obvious, but commentators wishing to avoid what follows from this—namely the establishment of the papacy—have suggested that the word rock could not refer to Peter but must refer to his profession of faith or to Christ.
From the grammatical point of view, the phrase "this rock" must relate back to the closest noun. Peter’s profession of faith ("You are the Christ, the Son of the living God") is two verses earlier, while his name, a proper noun, is in the immediately preceding clause.
As an analogy, consider this artificial sentence: "I have a car and a truck, and it is blue." Which is blue? The truck, because that is the noun closest to the pronoun "it." This is all the more clear if the reference to the car is two sentences earlier, as the reference to Peter’s profession is two sentences earlier than the term rock.
The previous argument also settles the question of whether the word refers to Christ himself, since he is mentioned within the profession of faith. The fact that he is elsewhere, by a different metaphor, called the cornerstone (Eph. 2:20, 1 Pet. 2:4-8) does not disprove that here Peter is the foundation. Christ is naturally the principal and, since he will be returning to heaven, the invisible foundation of the Church that he will establish; but Peter is named by him as the secondary and, because he and his successors will remain on earth, the visible foundation. Peter can be a foundation only because Christ is the cornerstone.
In fact, the New Testament contains five different metaphors for the foundation of the Church (Matt. 16:18, 1 Cor. 3:11, Eph. 2:20, 1 Pet. 2:5-6, Rev. 21:14). One cannot take a single metaphor from a single passage and use it to twist the plain meaning of other passages. Rather, one must respect and harmonize the different passages, for the Church can be described as having different foundations since the word foundation can be used in different senses.
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