Q. Peter writes in his first letter, “As you come to him [Jesus], the living Stone—rejected by humans but chosen by God and precious to him—you also, like living stones, are being built into a spiritual house.” What is a “living stone”? What does that mean?
The references to Jesus as a living stone, and to us his followers as living stones, actually look forward to the quotation from Isaiah that Peter offers shortly afterwards. In the original context in Isaiah, the “cornerstone” is a figure for justice. The correct lines for a stone building (i.e. the placement of all the other blocks) were all derived from a perfectly squared-off cornerstone that was laid down first. In the same way, God says, He will establish justice so that all of the Judeans can know whether their actions are “within the lines” or not. (“I will make justice the measuring line and righteousness the plumb line.”)
As often happens when New Testament authors see a Messianic meaning in an Old Testament prophecy, Peter is “escalating” the language so that the cornerstone (justice) becomes personified in Jesus. That’s what “living” means: An abstraction, justice, is now embodied in a person, Jesus the Messiah. He is, in effect, the “first block laid down,” and we who are “being built into a spiritual house” (that is, into a new kind of temple, as other New Testament writers also say) need to take our bearings and find our placement from Jesus. Not in a physical sense, but in the sense of moral purpose: “How can my life and actions fit in with what God has already started doing in the world through Jesus?”
We today probably aren’t very familiar with the approach to construction that involves first laying down a cornerstone. So let me offer a modern analogy. When a baseball field is laid out, the first thing put down is home plate. The foul lines are drawn out from the back of it. And those foul lines tell you whether a batted ball is “in” or “out.” The life, teachings, and example of Jesus establish the lines in our lives of what’s “in” and “out,” not just morally, but also in keeping with God’s expanding purposes in the world. He is, in effect, a “living home plate,” and we are a “living infield” and a “living outfield.”