This isn't referenced all that much in Isaiah. It appears quickly and then it disappears. It's not one of Isaiah's main symbols, but it's important because it's used later on in a famous New Testament parable to represent the foundation of belief in God. In Isaiah 28:16, God says "See, I am laying in Zion a foundation, a tested stone, a precious cornerstone, a true foundation." There are other passages in the Hebrew Bible relating to the cornerstone—Psalms 118:22 is particularly important—and references to the stone get repeated about six times in the New Testament. Matthew 21:42 is a good example, since it strongly implies that Jesus is himself the cornerstone: "The stone that the builders rejected is become the cornerstone."