A.T. Robertson Commentary Luke 20:17

"But he looked upon them, and said, What then is this that is written, The stone which the builders rejected, The same was made the head of the corner?" — Luke 20:17 (ASV)

He looked upon them (εμβλεψας αυτοις). Not in Mark and Matthew. First aorist active participle of εμβλεπω, to look on. It was a piercing glance. The scripture quoted is from Ps 118:22 and is in Mr 11:10; Matthew 21:42, which see for the inverted attraction of the case λιθον (stone) to that of the relative ον (which).