The Apostle Peter expounds Christ’s Vinedresser Parable of Matthew 21. He identifies the new nation that will bear kingdom fruit, and by using Old Testament quotes he gives us more commentary on the chief cornerstone. As it is written…
"Behold, I lay in Zion a chief cornerstone, elect, precious, and he who believes on Him will by no means be put to shame." [quote of Isaiah 28:16]
Therefore, to you who believe, He is precious; but to those who are disobedient,
"The stone which the builders rejected has become the chief cornerstone," [quote of Psalm 118:22] and "A stone of stumbling and a rock of offense." [quote of Isaiah 8:14]
They stumble, being disobedient to the word, to which they also were appointed.
But you are a chosen generation, a royal priesthood, a holy nation, His own special people, that you may proclaim the praises of Him who called you out of darkness into His marvelous light; who once were not a people but are now the people of God, who had not obtained mercy but now have obtained mercy. [I Peter 2]
Peter uses the pronoun "you" to identify the new nation. So the next question is who is Peter addressing in his letter? In context he addresses "you who believe." In opening the letter he addresses the dispersed believers in the churches through out what is now Asia Minor.
"Peter, an apostle of Jesus Christ, to the pilgrims of the Dispersion in Pontus, Galatia, Cappadocia, Asia and Bithynia, elect according to the foreknowledge of God the Father…" [I Peter 1:1]
Peter leaves no doubt to whom he is addressing. He identifies them as the elect, which means that any New Testament believer can claim the letter for his own. Therefore, the new nation of which Christ refers is his body, the church of the living God made up of all His people; a multitude that no man can number from ever kindred, tribe, nation and tongue, including Jews.
"The kingdom of God is not meat or drink but righteousness, peace and joy in the Holy Spirit." [Romans 14]