Luke 20:18

“Every one who falls on that stone will be broken to pieces, but on whomsoever it will fall, it will scatter him as dust (or ‘blow him away as chaff').”

And the stone will not only become the head of the corner, but it will also become a stone of destruction on which men will fall, like a pot on a hard stone, and be broken in pieces, and which itself will fall on men, as a stone may fall on pots, scattering them as dust. The picture may well have in mind the idea of a city which is being destroyed after siege, with stones being torn down and falling on the pottery beneath, while other pottery is seized and dashed (like the children - Luke 19:44) against stones. (There is an interesting Jewish proverb which illustrates this, "If the stone falls on the pot, alas for the pot; if the pot falls on the stone, alas for the pot!" It was one therefore to which they should have taken heed. However, where the pictures are used elsewhere in Scripture they refer to what happens to men (Isaiah 8:14; Daniel 2:34). He will thus be for both salvation and judgment. Some will be founded on Him and become strong, others will fall on Him, or be crushed by Him, and will be destroyed. Both in the comparatively near future and in the last Judgment (both are again brought together in chapter 21).

The picture is taken from a combination of Isaiah 8:14, ‘He will become a Sanctuary, and a stone of offence, --- and many will stumble on it, they will fall and be broken', and Daniel 2:34, ‘a stone was cut out by no human hand and it smote the image on its feet of iron and clay and broke them in pieces'.

As this verse is not cited by either Matthew or Mark in this context this may have been added by Luke from other sayings of Jesus, in order to give a satisfactory conclusion to the passage, for in contrast with them he has omitted ‘this was the Lord's doing, and it is marvellous in our eyes' (Mark 11:11; Matthew 21:42). By it he brings together salvation and judgment in a way quite in keeping with the parable, and consonant with the whole wider context of the passage. Compare also 1 Peter 2:7 where similar ideas to those here are linked.