Nicely explained Oilburner. Peter himself identified the rock-mass (petra) on which the congregation is built as being Christ Jesus.
(1 Peter 2:4-8) As you come to him, a living stone rejected by men but chosen, precious to God, 5 you yourselves as living stones are being built up into a spiritual house to be a holy priesthood, in order to offer up spiritual sacrifices acceptable to God through Jesus Christ. 6 For it says in Scripture: “Look! I am laying in Zion a chosen stone, a precious foundation cornerstone, and no one exercising faith in it will ever be disappointed.” 7 It is to you, therefore, that he is precious, because you are believers; but to those not believing, “the stone that the builders rejected, this has become the chief cornerstone” 8 and “a stone of stumbling and a rock of offense.” They are stumbling because they are disobedient to the word. To this very end they were appointed.
Peter was showing the rejecting of Jesus was a fulfillment of prophecy.
(Psalm 118:22) The stone that the builders rejected Has become the chief cornerstone.
