The cornerstone was the crucial first stone that set the line and held a building together. Scripture calls Christ the chief cornerstone — the foundation on which the whole church is built and aligned.
Though rejected by the builders, he became the head of the corner. Everything in the life of faith is measured and steadied by him; build on any other foundation, and it will not hold.
The Cornerstone in Scripture
And are built upon the foundation of the apostles and prophets, Jesus Christ himself being the chief corner stone;