The stone which (λιθον ον). Inverse attraction of the antecedent into the case of the relative.

The builders rejected (απεδοκιμασαν ο οικοδομουντες). From Psalm 118:22. A most telling quotation. These experts in building God's temple had rejected the corner-stone chosen by God for his own house. But God has the last word and sets aside the building experts and puts his Son as the Head of the corner. It was a withering indictment.