“Therefore, I say to you, the kingdom of God will be taken from you and given to a nation bearing the fruits of it. And whoever falls on this stone will be broken; but on whomever it falls, it will grind him to powder.” Now when the chief priests and Pharisees heard His parables, they perceived that He was speaking of them. But when they sought to lay hands on Him, they feared the multitudes, because they took Him for a prophet.”
This quote about the Stone rejected by the builders is Psalm 118: 22-23, taken from the Septuagint. The Stone is Christ.
Exodus 17:6 I will stand there before you by the rock at Horeb. Strike the rock, and water will come out of it for the people to drink." So, Moses did this in the sight of the elders of Israel.
1 Corinthians 10:3-4 They all ate the same spiritual food and drank the same spiritual drink; for they drank from the spiritual rock that accompanied them, and that rock was Christ.
In Isaiah the Lord says: “And if thou shalt trust in him, he shall be to thee for a sanctuary; and ye shall not come against him as against a stumbling-stone, neither as against the falling of a rock: but the houses of Jacob are in a snare, and the dwellers in Jerusalem in a pit. Therefore, many among them shall be weak, and fall, and be crushed; and they shall draw nigh, and men shall be taken securely. Isaiah 8: 14-15 LXX).
Christ is the Rock of the Church, but He is also the rock or stone that was rejected. It is interesting to note that the place of the crucifixion was once a rock quarry. This is testified-to by ancient writers but also confirmed by modern geologists and archaeologists. The reason for the “skull” shaped feature of the place was due to the good rock for building having been already removed, and the “rejected” stone remaining in place.
Christ is the rejected stone, yet He is, in actuality, the strongest stone of all. The corner stone was always supposed to be the strongest and best stone. The whole building depended on this stone, and that's why the cornerstone is always blessed when we begin new construction. The building here, is of course, the church. St Paul understands it this way saying “Now, therefore, you are no longer strangers and foreigners, but fellow citizens with the saints, and members of the household of God, having been built upon the foundation of the apostles and prophets, Jesus Christ Himself being the chief cornerstone” (Ephesians 2:19-20).