In architecture, the capstone is the rock or stone placed on top of a wall. Unlike the cornerstone, which is the base of the structure and an important stone of the foundation, the capstone is the final stone placed on top that helps hold the structure together. The capstone, like the cornerstone, is an important metaphor for Jesus and His prominence as Head of the church and the kingdom of God.
In the Old Testament, Psalm 118:22 and Zechariah 4:7 mention a capstone. Zechariah correlates the word with the completion of the temple as Zerubbabel sets the capstone (Zechariah 4:7). The Lord tells Zechariah, “The hands of Zerubbabel have laid the foundation of this house; his hands shall also complete it” (Zechariah 4:9, ESV). In Psalm 118:22, the word could be translated as either “cornerstone” or “capstone.” This is the verse that Jesus quotes in His parable of the vineyard.
As in Psalm 118:22, the word for “cornerstone” in Matthew 21:42, Luke 20:17, Acts 4:11, Ephesians 2:20, and 1 Peter 2:7 could technically be translated as either “capstone” or “cornerstone.” The word in Greek can mean “head, chief, or cornerstone,” but the word carries a connotation similar to that of capstone. For instance, in the 2001 edition of the New International Version, Matthew 21:42 states, “The Stone the builders rejected has become the capstone,” with a note indicating that the word in question could also be translated as “cornerstone.” Similarly, in the same version, the word in Acts 4:11 and 1 Peter 2:7 is translated as “capstone.” A cornerstone and a capstone are different stones with different functions, so how can the words be interchangeable? A verse that helps clarify the confusion is Luke 20:18, in which Jesus states, “Everyone who falls on that stone will be broken to pieces, and when it falls on anyone, it will crush him” (ESV). Someone could fall on a cornerstone, given its location at the base of a building. In contrast, a capstone could fall on someone since it crowns a building. It is likely that Jesus indirectly refers to Himself as both the capstone and cornerstone here.
When Peter stated that “Jesus is ‘the stone you builders rejected, which has become the cornerstone,’” he meant that, although Israel had rejected the Messiah, Jesus is still God’s choice. Jesus is supreme because salvation is only found in Him (Acts 4:11–12). In Ephesians 2:20, Jesus is described as the “chief cornerstone” of the church, but He can also be seen as the capstone since “in him the whole building is joined together and rises to become a holy temple in the Lord” (Ephesians 2:21). Jesus is the foundation of the church but also the capstone that holds everything together (Colossians 1:17).
Christ is both the cornerstone and capstone. He is the foundation of our salvation, what we believe, and our future hope (see Hebrews 6:18). He is also the capstone, holding all things together and keeping our salvation secure (John 10:28). He is the beginning represented by the cornerstone and the end represented by the capstone (see Revelation 22:13). Using architectural terms such as capstone and cornerstone provides helpful images to describe Christ and the salvation and security He provides.