Why does Peter call Jesus the chief cornerstone?
Peter calls Jesus the chief cornerstone because the Old Testament analogy identifies Christ as the stone the builders dumped out, the head of the corner who holds all the architecture together. That stone was Christ, the rock of salvation, not Peter. The legend illustrates how the true cornerstone was ignored and cast aside.
Les explains that Peter is using an Old Testament analogy: Christ was to be the chief cornerstone, the head of the corner. Scripture constantly presents Christ as the rock and the stone—the rock of our salvation—not Peter. Les then relates a legend, not Scripture, about Solomon's temple: everything was pre-cut at the quarry, so no hammer or chisel was heard at the building site. The chief cornerstone was brought in ahead of time, but the engineers and architects did not recognize it, so they dumped it in a vacant lot where weeds grew around it. In arch architecture, the top stone holds everything together; that is what Christ was to have been, but the builders cast that stone aside. People walking through the vacant lot would bump into it in ignorance.