To us, Jesus' comments after the story, in verses 17–18, may seem difficult. But to Luke's readers they made eminent sense. For Jesus is fusing together here three verses with which they were very familiar. The New Testament quotes them often. Perhaps they come to Jesus' mind here because they are all about stones. And in the Aramaic language that he spoke, the word for 'stone' and the word for 'son' sound almost identical.
The first quotation is from Psalm 118, and speaks metaphorically of the construction of a house. The masons building the house discover an oddly shaped stone that won't fit in the wall. At first they discard it, but then when they get to the very top of the building they realize that this is just the piece of rock they need to complete the supporting arch, the brick without which the whole edifice would otherwise collapse—the chief cornerstone.
In its original setting this psalm applied the metaphor to the king of Israel on his return to Jerusalem after a successful military campaign. The pagan nations had treated the king of Israel with contempt, and they discarded him like a worthless pebble. But now God has vindicated his anointed one and exalted him over his enemies. So the stone the builders had rejected has become the capstone. 'It's the Lord's doing and it's marvellous in our eyes,' they sang.
But to the Jews of Jesus' day this entire psalm was interpreted messianically. Indeed, we encounter a chorus of it on the lips of the crowd as they welcome Jesus triumphantly into Jerusalem on Palm Sunday: 'Blessed is the king who comes in the name of the Lord' (Luke 19:38).
So Jesus is pointing out the full implications of Psalm 118 to these so-called Bible students who were challenging him. 'If, as you believe, this is a messianic prophecy, then don't you see what it implies? It implies that the powerful men of this world will repudiate the Messiah just as those pagan nations repudiated the king of Israel
