Human beings love using metaphors, comparisons between two things that are unlike to bring out some special way in which they are alike.  In I Peter 2:4-12, the author piled on a series of metaphors and quotations from the Old Testament to explain, first, who Christ is and, second, who Christians are.  The first metaphor he used was that Christ is a living stone, the cornerstone in fact.  Christians in turn are built upon him as living stones and are also a chosen race, a holy and royal priesthood, a holy nation, a people for God’s own possession, and God’s people.  All of these privileges are the result of God’s mercy not of Christian’s merit.