Have you not read this scripture: 'The stone the builders rejected has become the cornerstone. This is from the Lord, and it is marvelous in our eyes'?" (Mark 12:10-11 NET) The cornerstone is the first stone set in the construction of a masonry foundation. It is important since all other stones will be set in reference to this stone, thus determining the position of the entire structure. (2) The cornerstone was usually one of the largest, most solid, and most flawlessly constructed of any of the stones of a structure.