Biblical References:
The concept of a "cornerstone in Zion" is a significant biblical metaphor found in both the Old and New Testaments. The primary reference is Isaiah 28:16, which states: "So this is what the Lord GOD says: 'See, I lay a stone in Zion, a tested stone, a precious cornerstone, a sure foundation; the one who believes will never be shaken.'" This prophecy is foundational in understanding the messianic symbolism associated with the cornerstone.

Old Testament Context:
In the context of Isaiah, the cornerstone represents a firm and reliable foundation laid by God Himself. Zion, often synonymous with Jerusalem, is depicted as the spiritual center where God establishes His presence and purposes. The cornerstone signifies stability, strength, and the beginning of a new construction, symbolizing the establishment of God's kingdom and His covenant with His people.

New Testament Fulfillment:
The New Testament writers interpret the cornerstone prophecy as fulfilled in Jesus Christ. In 1 Peter 2:6, the apostle Peter quotes Isaiah 28:16, affirming Jesus as the cornerstone: "For it stands in Scripture: 'See, I lay in Zion a stone, a chosen and precious cornerstone, and the one who believes in Him will never be put to shame.'" This passage highlights the belief that Jesus is the foundation of the Church and the fulfillment of God's promises.

Similarly, the apostle Paul in Ephesians 2:20-22 describes the Church as "built on the foundation of the apostles and prophets, with Christ Jesus Himself as the cornerstone. In Him the whole building is fitted together and grows into a holy temple in the Lord." Here, the cornerstone metaphor extends to the unity and growth of the Church, with Jesus as the essential element that holds everything together.

Symbolism and Theological Significance:
The cornerstone in Zion symbolizes Jesus as the essential and foundational element of faith. It represents His role as the Messiah, the one who fulfills the prophecies and establishes a new covenant. The imagery of a cornerstone conveys the idea of strength, permanence, and alignment, as all other stones in a building are set in reference to it.

Theologically, the cornerstone metaphor emphasizes the exclusivity and sufficiency of Christ as the foundation of salvation. Believers are called to build their lives upon Him, ensuring that their faith is anchored in His teachings and redemptive work. The cornerstone also serves as a dividing line, as those who reject it stumble, as noted in 1 Peter 2:7-8: "Now to you who believe, this stone is precious. But to those who do not believe, 'The stone the builders rejected has become the cornerstone,' and, 'A stone of stumbling and a rock of offense.'"

Conclusion:
The cornerstone in Zion is a profound biblical image that encapsulates the essence of Jesus' mission and the establishment of God's kingdom. It serves as a reminder of the stability and security found in Christ, urging believers to align their lives with Him as the true foundation.