The corner stone is the foundational stone for a building. It is the first stone laid during a building project. Jesus was making a point to the religious that day. Even those who are slightly offended by the words of Christ are like ones falling on the stone and being broken. Those that hate and despise his truth because it does not fit their lifestyle will be crushed by His message.
The Words of Christ are powerful and sharper than any two-edged sword. They cut to the heart going in and coming out. Those that are broken and desire to receive will be changed. Those that are not broken and despise his truth will fall under the Lord's judgement. The Religious sects listening to Jesus during this time understood quit well that Jesus was speaking about them.
Jesus is the cornerstone of life. He is the foundation of all that is, was, and will ever be. His truth is real and will forever remain. It can either break us to the point of repentance and change or it can crush us to thousands of pieces through his judgment. We desperately need him. We desperately need His word to change us. We desperately need the message.