The fundamental point of ecclesiology is encapsulated in the lyric: “The church’s one foundation is Jesus Christ her Lord.” In other words, God’s people find their origin, grounding, direction, and security in Christ. Without a firm grasp of this truth, the church devolves into a man-made society governed by the whims of finite creatures, not the Word of the creator God Himself. Scripture makes this point in many ways, but it can also speak of Peter and the other apostles as the foundation of the church (Eph. 2:19–20), with Jesus being the “foundation of the foundation” because He is the cornerstone (Acts 4:11). The apostles function as the foundation of the church through their writings — the New Testament — which reveal and proclaim the church’s Lord. Key to this foundation is Peter’s confession of Jesus as the Christ (that is, Messiah; Matt. 16:16–18), a divinely-revealed truth that sums up the Gospel. John Calvin writes: “The designation Christ, or Anointed, includes both an everlasting Kingdom and an everlasting Priesthood, to reconcile us to God, and, by expiating our sins through his sacrifice, to obtain for us a perfect righteousness, and, having received us under his protection, to uphold and supply and enrich us with every description of blessings.” Yet Peter did not fully know what he was saying when he first declared that Jesus is the Messiah — the son of David who builds God’s house (2 Sam. 7:1–17). This is evident in today’s passage, wherein Peter is rebuked for misunderstanding Jesus’ work shortly after being praised for recognizing His office. Once it is out in the open that Jesus is indeed the Christ, our Lord begins to teach plainly His need to die for the sins of His people (Matt. 16:21). At first this is unacceptable to Peter; he does not want a Messiah who is anything but a mighty ruler who leads Israel to an earthly victory (v. 22). But there can be no conquering king until the Savior first takes the curse off His nation at Calvary (Gal. 3:10–14). Peter stumbles and, like Satan in the wilderness, offers Jesus a crown without the cross (Matt. 4:1–11). Jesus has none of this, for He is committed to His Father, whose covenant demands that sin’s debt be paid in full (Ex. 34:6–7).