Jesus said to them, “Have you never read in the Scriptures, The stone that the builders rejected has become the cornerstone. This came from the Lord, and it is marvelous in our eyes?’a Bible see other translations
From Ps. 118:22-23

the cornerstone.” The quotation comes from Psalm 118:22. The Greek text literally reads, “the head of the corner,” not “the cornerstone.” However, the stone that is “the head of the corner” can be the cornerstone. However, the phrase “the head of the corner,” can refer to two different stones, the cornerstone and the capstone, and there is some discussion about what is meant. “The phrase ‘head of the corner’ can indicate one of the large stones near the foundations of a building which by their sheer size bind together two or more rows of stones,” or it can “refer to the final stone which completes an arch or is laid at the top corner of a building.”a

There is some scholarly discussion about which stone is meant, and it is even possible that Christ is thinking of both stones, because when he says, “the one who falls on this stone will be broken to pieces, but on whomever it falls it will grind to powder” (Matt. 21:44; cp. Luke 20:18), he seems to be referring to both stones. A person would fall on or stumble over the “cornerstone,” but the stone that could fall on someone and grind them to powder would be the capstone. Both the cornerstone and the capstone are important to the building and thus the analogy is that Christ, who was rejected, has become of supreme value. Translators can only pick one of the two words for their translation, and like most English versions, the REV has chosen “cornerstone” to be in the text.b

Psalm 118:22 is very important in identifying Jesus Christ as the Messiah, and it is quoted or referred to six times in the New Testament (Matt. 21:42; Mark 12:10; Luke 20:17; Acts 4:11; 1 Pet. 2:4 and 2:7).

“the Lord.” The Shem Tov Hebrew manuscript has “Yahweh,” the personal name of God, and a rabbinic abbreviation for it appears in the Hebrew manuscript of Matthew as well as in the verses of the Old Testament that Matthew quoted. There is evidence that Matthew wrote his Gospel in Hebrew and used the name Yahweh (see commentary on Matt. 3:3).

J. B. Taylor, “Cornerstone,” New Bible Dictionary, 228.
Taylor, New Bible Dictionary, 228.

Commentary for: Matthew 21:42