What is the rock that Jesus promisee that the Church would be built on?

In Matthew 16:18 does the Rock represent Christ? Or does it mean Truth? Or does it mean the Word of God? If it is Christ, can you give Scripture to prove this?

No doubt, our questioner is aware that this is a much disputed passage; though personally we believe the true meaning is not far to seek, in the light of the context and of the general analogy of Scripture. The disciples’ answer to the Lord’s question, “Whom do men say that I the Son of Man am?” led on to His second question, “But whom say ye that I am?” The Lord desired to hear from their own lips their confession of Him. All were addressed, but one—Simon Peter—replied, “Thou art the Christ, the Son of the living God” And the Lord pronounced him—”Simon Bar-jona”—blessed (lit, happy), for this had not been learned in the schools of men, but direct from His Father. Not only so, but as Simon Peter had confessed his Lord’s Name before His fellow-disciples, now on the principle of Luke 12:8, the Lord confesses his name—”And I say also unto thee, that thou art Peter.” In other words He confirms to him the name of Petros or a Stone, which He had conferred on him at his introduction by his brother Andrew (John 1:41).

Moreover, the Lord has something more important to dwell on, namely, the noble, God-given confession by Peter of His true Messiahship and glory as the Eternal Son—something bigger than a “Petros,” a stone,—a “Petra,” a rock. This distinction is common in classical Greek, and though in Aramaic, the language in which our Lord usually spoke, the difference is not shown, both words being Cepha, the fact that the inspired evangelist, in translating, brings out the classical difference, seems to show clearly that the Spirit of God intended the difference to be preserved. Peter is never certainly spoken of as a rock (petra) in any other place of Scripture, but he himself speaks of Christ as the rock (petra) of offence, and this is the word used in 1 Corinthians 10:4—”They drank of that spiritual rock (petra) that followed them, and that rock (petra) was Christ.”

Peter was “a living stone” along with his fellow disciples, but Christ was the living Rock. Our Lord’s words accordingly are not, “Thou art Petros, and upon thee I will build my church,” but “Thou art Petros and upon this rock (petra) I will build my church.” Perhaps we shall be told this is only Protestant and heretical doctrine. But was then Hilary, bishop of Poitiers in the 4th century, heretical? and yet he writes, “The rock petra is the blessed only rock faith—confessed by the mouth of Peter.” Was Jerome heretical, who writes, “Christ has founded His church on this rock, and it is from this rock that the Apostle Peter has been named”? Chrysostom whom we cannot admit was a heretic, says, “On this rock I will build my church, that is on the faith of the confession of Peter,” and so Ambrose of Milan, Basil of Seleucia, and indeed over forty of the early fathers and ecclesiastical writers (not all, we presume, Protestants or heretical teachers) held that the rock was Christ Himself as revealed in the confession of Peter. So Augustine of Hippo: “On this rock (petra) I will build my church, not on Peter, the stone that thou art, but on the rock that thou hast confessed, I will build thee, who in this reply standest for the church.” We may thank God that we have something more stable than vacillating Peter upon which to build for eternity.