What does Matthew 21:42 mean?

Jesus once more asks a group of Israel's powerful and well-educated religious leaders if they have ever read a particular passage from the Scriptures. He knows they have, but He asks the rhetorical question to show that they have missed the point of what they have read and studied.

The passage Jesus quotes comes from Psalm 118, one of the psalms used in the Passover season. Jesus is referencing verses 22–23, which are found just before the words used to praise Him as He entered Jerusalem on Palm Sunday (Psalm 118:25–26; Matthew 21:9). The translation used by Jesus matches that of modern English Bibles. These are words these religious leaders were angry to hear from the crowd, and from the children who later repeated them (Matthew 21:15).

Jesus applies these Old Testament words to Himself. He is the stone the builders rejected. The builders are Israel's leaders, including the chief priests and Pharisees standing near Him. Though rejected by them, the stone, Jesus, has become the cornerstone or "head of the corner," the most important stone in the structure. Prior to modern building techniques, it was extremely difficult to make the ground under a building perfectly level. Instead, whichever corner was lowest would be the location of the strongest, most important stone—which effectively held up the entire structure.

Alternatively, scholars suggest the phrase refers to the final keystone at the top of an arch. The Greek phrase is kephalēn gōnias, literally meaning "head of the corner." In either case, it is the stone on which the entire structure ultimately relies on to remain upright.

He adds that this is the Lord's doing, meaning that the rejection by merely human leaders could never have stopped it. More than that, it is "marvelous in our eyes." Jesus taking His place as the Messiah is ultimately a beautiful and pleasing work of God and not something engineered by any group of human beings.